Another thing you might do is not introduce food or meals as being "vegetarian". It sounds like he has the idea that vegetarian food is going to be icky, so I suspect any time he's fed something identified as vegetarian, he'll insist that he doesn't like it (8 year old logic).
I would just feed him what he normally eats, but without meat. An example: you can make a hamburger casserole without the hamburger. Use the same spices, etc., but put in beans (or corn or extra noodles, etc) instead of hamburger. You can use fake bacon on BLTs instead of regular bacon. I think you get the idea.
Unless he's used to eating big slabs of steak, chicken, etc., then he shouldn't notice that the meat is missing. After you've found several meals he likes, you might start calling them vegetarian. I think there's a thread on the parents board where people list what they feed their children every day. That can give you a lot of idea.
Another thing you might try is to not insist he be vegetarian outside of the house. Let him choose to eat meat if he has dinner at a friend's house. He might feel less threatened by eating meatless if he knows that he can "escape" it every once in a while. Once the weirdness wears off, he might even surprise you by choosing to be a vegetarian all the time.