I am the same and DS started to copy me. I told him he shouldn't chew his nails and that I wanted to stop as well. I asked him to tell me to stop chewing mine if he sees me. We went through it several times when he was chewing his nails and now he doesn't at all. But he does tell me to 'please stop chewing your nails mum!'. I figure if he can't I can't either!
Other than that you can get that nail polish that tastes awful. It does work (I used it as a kid) but it also isn't very nice when you are eating sandwiches. LOL