What do they do with the stuff they take out?

I'm walking past this pizza joint on 4th Ave. downtown, and they got this sign outside the store. They make vegan pizza and they make gluten free pizza. I didn't have time to go in, but I was wondering: if I asked them to put some of the gluten they take out of the other pizzas on mine, could they? Would they? What do they do with the gluten they take out of gluten pizza?