I am in the same boat man. My school doesn't allow food or drinks anywhere in the school but the lunch room, you just need to beat the system. There is me and my friend who have succesfully dont it. Time your meals so that you eat rite before class, then make a shake to keep in your locker. During class just ask to go to the bathroom and chug the shake. Then go to you lunch period.
I am lucky I have the perfect schedual so everything works out for me. 7am breakfast, 10am (3rd period) shake or grilled chicken, 1pm lunch in school. I just ask to go to the bathroom then bring my food in there and feast away. My friend always eats in class but I hate doing that, takes to long and you always have to watch out for teachers.
The diabetic thing works to, my brother was actually a diabetic and he use to eat 24/7 in class. I drafted this idea for a while and told them it was hereditary meaning I had it, I would really bust their chops by bringing like crazy gormet food in and just tell them my doctor is making me eat it heh.
There is always a way to manage 6 meals a day and they can all be to the strictest of guidlines, you just need to manage your time and figure out a routine. I manage 7 meals a day with minimal problems.