For now I can offer in support of this claim about non-placebo placebos only a collection of quotes with links to their original sources. The first two quotes are specific to the Gardasil vaccine, but the others more general.

Footnotes usually omitted. My emphasis unless otherwise specified. Quotations are in offset italics.

The FDA allowed Merck to use a potentially reactive aluminum containing placebo as a control for most trial participants, rather than a non-reactive saline solution placebo.[1] A reactive placebo can artificially increase the appearance of safety of an experimental drug or vaccine in a clinical trial. Gardasil contains 225 mcg of aluminum and, although aluminum adjuvants have been used in vaccines for decades, they were never tested for safety in clinical trials. Merck and the FDA did not disclose how much aluminum was in the placebo.

Merck and the FDA do not reveal in public documents exactly how many 9 to 15 year old girls were in the clinical trials, how many of them received hepatitis B vaccine and Gardasil simultaneously, and how many of them had serious adverse events after being injected with Gardasil or the aluminum placebo. For example, if there were less than 1,000 little girls actually injected with three doses of Gardasil, it is important to know how many had serious adverse events and how long they were followed for chronic health problems, such as juvenile arthritis. (ibid.)

This part (see below, quoted) of an essay by Teresa Binstock is found half way down the page of the source linked below the quote. I notice the suggested motive for not using a simple saline placebo. Seems a strained argument, but not when I recall reading of the troubles finding a good adjuvant for other vaccines. (Adjuvants increase the antibody output caused by the vaccine’s antigens, which makes the vaccine work better.) Merck, the author is suggesting, suspects their adjuvant may cause more side effects than the antigens in the vaccine. If they tested the real vaccine (with its mix of antigens and adjuvant) against real placebo, they would not be able to explain away any side effects that might show up more frequently in the test group than the control. But this way, silently assuming that the adjuvant is entirely safe by calling it placebo, side effects actually due to the adjuvant will appear in both groups in about the same number and thus be attributed to something other than the vaccine.

I have removed a large number of footnotes from the quote. See the original to find significant supplementary support for these claims.

An FDA document provides evidence that in most, indeed in nearly all pre-market testing of Gardasil, aluminum compounds that were in the vaccine and vaccinations were also in the placebo injections. As an autism-parent summarized: "...in the double blind trials on Gardasil, they had aluminum in the placebo as well as the HPV vax."

Although a Merck employee's review states that aluminum adjuvants are safe, other researchers state differently, eg, "Among the vaccine's potentially toxic components are the adjuvants aluminum hydroxide..." Furthermore, aluminum is increasingly implicated in neurodegeneration.

These several findings suggest that Merck's testing was deliberately designed to neutralize adverse effects from aluminum injections, particularly in the context of vaccination-reactions. As of this morning, EnvironmentalHealthNews (EHN) had 61 articles about Gardasil. Many news articles focus upon one or more individual's adverse reactions to Gardasil, and the total number of Gardasil-induced adversities continues to increase.

The following is from Dr. Lawrence Palevsky’s part in a dialogue with Dr. Joseph Mercola on the general topic of vaccines. As both doctors have come over time in their practices to change their views on vaccination, and as both write and speak extensively on the topic, I think Dr. Palevsky’s comments here, although without reference or footnotes, should be given preliminary credence. This was my jumping off point for thinking carefully about immunization. To date I have not found any evidence to contradict Palevsky in this interview. Indeed, in the section above this, you find specific and sourced support for his statements from several people, and if you follow up the links, you will discover appropriate medical and scientific studies. I will give more specific and narrow evidence following this.

…in order for us to really delve into those studies [alluding to Dr. Offit’s claim that 20,000 studies prove vaccines to be safe], we have to look at who supported the studies. What was the study design? What were the control groups? How big was the actual number of kids or adults that was used in those studies? I think we will see that in most of those studies, the actual safety has never really been proven.

One of the reasons that I think we can fairly say that is that the vaccine manufacturers and the conventional medical organizations have not done studies that compare vaccinated to unvaccinated children. In order for us to really know if children who were vaccinated are having an adverse effect from a vaccine, we have to use a placebo group that's given an injection of maybe normal saline to evaluate whether or not they developed the same symptoms that children who were vaccinated may develop after they're injected with the vaccine.

Those studies are not done. They're not done because the conventional medical system says it's unethical to leave kids unvaccinated for any length of time. But, most of the vaccine safety studies that are being done last anywhere between one and four weeks anyway. The kids are followed within those one to four weeks. Then, they're not followed in a very detailed way to recognize whether any of their health outcomes could be related to the vaccine that they got one to four weeks ago. {Case in point: }

What ends up happening is they compare the incidence rates of these vaccine reactions or these symptoms that kids get after they're vaccinated to how often those symptoms are seen in the general population, to check and see if this vaccinated group is in any way getting an increased incidence of these symptoms than the general population would get. But the fact of the matter is that the general population is vaccinated, so they're comparing a vaccinated group with a vaccinated group.

…they are not following children long enough to know whether in three months, six months, three years, six years, or 10 years, there could be some autoimmune antibody or some immune challenge that happens to the body that lingers or that just sits there as a genotypic effect. There's a change in the genetics, there's a change in the DNA, that doesn't necessarily manifest itself until years later because of other stressors, perhaps even from another vaccine that comes years later. (Ibid.)

This excerpt from a medical study just appears routinely as part of a paper on vaccines:

Two vaccines, one containing pertussis toxin (JNIH #7), the other pertussis toxin and filamentous hemagglutinin (JNIH #6), were compared with a placebo which contained the carrier solution of the vaccines (formalin, thimerosal and aluminum phosphate). [That would be formaldehyde, mercury and aluminum. See the Palevsky quote above for the tortured reasoning that could make people think the carrier was a better placebo than saline solution. Or, above that, the Teresa Binstock observations.]