I don't see a problem with the students taking turns at playing the part of the waiters. There's nothing particularly difficult or arcane about the vocabulary or phraseology of waiters, and your students will have come across the necessary phrases in their own language and personal experience of being waited on. Just because they are not training to be waiters is no reason not to involve them in a little enjoyable role-play. Encourage the "customers" to ask about the various items on the menu [Does the ravioli have any nuts in it?], and tell the "waiters" that they can be as inventive as they like in their responses.