Lots of great advice from everyone..
fifi...you come across as a really down to earth concerned parent who wishes the best for her child. I don't think that there is anything better at ensuring his balance than for you to really, make yourself available to talk to him. I think if he's playing Warcraft, watching Borat and doing all the other things kids do without getting all guilted out, then so far, so good. As one of the other posters mentioned, he's entering an awkward time of his life. He will probably be more likely to come to you regarding girls, school etc...than his father if he knows in advance all the WTS advice his father will probably give him. I would ask a lot of questions and do a lot of listening and establish that he can trust you and talk to you about anything no matter what.
There is a really good book call "The Prophet" Kahlil Gibran that covers a lot of ground about life. It's not super religious or controversial despite the name....and is very well written. I'd give it a once over and see if you think he might like the more spiritual less religious aspect of it.
Another poster wrote about keeping him active in sports, guitar etc...that was a biggie for my oldest son. I made him play little league baseball and go out for football in high school....he wasn't very good but it didn't matter....he later thanked me and said the team aspect and comraderie did wonders for his social life. Ultimately if he can actually experience the normal things that most kids get to...then getting baptised won't be so attractive.
I would try to impress on him not to even consider getting baptised until after he is finished with college. If you can do that, I think when he reaches 22 you'll find that he will embrace life instead of run from it.
Best of luck to you and the other posters with the 12 year olds!!!
r's hubby