Now, as an adult --- I would need to be tricked
Psychosomatic affects are real, real to the person. It's hard not to help it sometimes and it's mostly out of your control until you can trick your head back into what is real.
Not saying you should trick him, I don't agree with tricking a child...but double blind and letting him know it's double blind...I don't see why your doctor won't try it that way. I think they do double-blind but someone in the office does know what is what (just not the parent, doctor, nurse in with the person).
That being said --- I had an adult friend who did desensitization for peanuts. They put the peanut in pudding so you just swallowed, no chewing. Why? B/c apparently the allergen still "takes like hivey weirdness" She noted she could eat small amounts of peanut from the study, but it was a horrible horrible taste.
I think there is something to being able to still taste the allergen...and then reacting based off the taste even if you aren't really truly reacting. It's a body/memory thing, no?
Adrienne