It *sounds* like this may not be an issue, but I'll throw it out: is it possible that your son may have some unidentified food allergies? Though were that the case, he'd be allergic to stealth tofu, too...

If that's NOT an issue, it may well be, as you noted in your original post, that he may have a particularly sensitive sense of taste. I read somewhere that something like 10% of the human population can be classified as "supertasters," that is, people who have particular sensitivity to bitter and salty tastes. On the other hand, if he likes junk food... : )

Perhaps it's possible that some of his pickiness is a reaction to outside influences, his peers who think vegetarianism is "weird"? As you said, it's hard to buck the norms when you're young.

Just some thoughts. Good luck with your son. Hopefully he'll grow out of it. FWIW, my younger brother was also a very picky kid, and when I became a vegetarian at age 16 (he was 12) he absolutely refused to eat anything I cooked that had tofu or other soy products in it-- it was "weird." Anyway... I fixed him good. I made a lasagna for dinner one night that had a filling of spinach and tofu, with a white sauce (made from cow's milk)layered with tomato sauce and noodles. Could my brother tell the difference between the tofu and the ricotta cheese I told him it was? Nope. He loved it. Ate many servings. I think I told him the truth when he was in college, by which time he'd become a semi-vegetarian neo-hippie anyway.