rcopper beat me to it again. "forced socialization" is probably the best route. they do live only a short time and wasting it being afraid is not fun. but here's another method that might be a little less stressful. get a hoodie and put the rat in the front pocket or hood and sit in a room (watch tv, read a book, do homework, listen to music, whatever) with him with you for at least 20 mintues, longer if you think the both of you cna afford the time. AT LEAST once a day but the more you this the faster the socialization. if you don't have a hoodie, cacoon yourself in a blanket on a couch or something and put him in there. he'll have more room to run and freedom to play this way but he'll still be with you. remember though that he may and probably will pee and poop the first few times to don't do this 20 mintues before you need to leave to go out to a fancy concert of something or use a blanket or hoodie that you can't afford to hav chew holes. after a few sessions (2-3) of this offer him food as well. i foudn popcorn and m&m's to a fav. but the tops off pudding cups seems to be the most successful. you hold the top and he has to lick off the chocolate/vanilla/tapioca/etc making sure he know's it come from you.
and of course the best way to make this the fastest ever is for him to learn by example. if you have other rats take one or all of them out with you after the first session or two and let them interact. offer food to everyone and the new boy will learn through them as well as his own experiences that you're actually pretty cool. with the help of other rats and the method explained above i have never failed, even with serverely abused rats that had every reason to be afraid and aggressive and no reason to trust.
as a side note (though i've never had problems with it) if you're worried you will be bit during socialization wear thicker clothes and shoes. but, like i said, i've never had a problem in this area. the only times i've been really bite (not hand held in the mouth or directed one way or the other which is nearly always very gentle) was when i reached into a timid mother's nest to check on babies. oddly enough this mother's sister (who had a litter herself the day before) would place her babies in my hand when i went to check on them then go out for a run in the room. different personalities eh...
anyway, try that and tell us how it goes. try the others suggestions as well and maybe you can find something even better. hope everything goes well.