Hi K.,
The good news is that there are more and more options out there.
I don't know where you live, but there is a bakery in Kennett Square, PA called Sweet Christine's. She is a gluten-free bakery, and she tries to make options that are kid-friendly. She has chocolate chip cookie kits where all you have to do is add egg and water, and the cookies are good! She makes bread, pies, muffins, bagels, cakes, etc. She also makes pizzas in individual sizes and sandwiches that kids can pack in their lunches that don't look different from other kid's foods. Even if you don't live close, I'm sure you can get her number from her website and order items. She developed this bakery because her daughter has celiac disease, and a portion of all of her proceeds goes to celiac disease research. (No, I don't work for Sweet Christine's, just found her products a Godsend)
I also got a book from my local library about cooking gluten-free, and it was very helpful. There are also special enzymes they can take 30 minutes before eating that will help him digest the gluten inside the stomach and help it pass through the intestines easier and reduce his discomfort when coming in contact with glutens.
I think you'll notice a great improvement in his overall health and attention. The reason my doctor tested my daughter was due to her ADHD and having stomach pain. She is a picky eater, too, but if certain foods made your stomach hurt, you might be picky, too! There is a significant link between ADHD and Celiac disease, according to my doctor.
Even if the endoscopy doesn't show anything conclusive, I'd recommend at least limiting his gluten. He could be gluten-sensitive, but not have the full blown disease.
We didn't find out about my daughter's problem until she was 12 or 13, and by that time, it was difficult to get her to cooperate with the diet change. If the problem is severe enough, he'll probably WANT to stay gluten-free, but if it is just mildly uncomfortable, he might not like the change much. It does make you say NO to alot of "regular" foods, but it is more healthy for him (and all of us, for that matter) if he steers clear. In fact, if the whole family goes gluten-free, everyone will feel better, have more energy, and probably lose weight! At least that is what happened in our family!
Good luck.
L.