As you can export your models in SKP format, maybe this can interest you ;)
http://www.l4d.com/blog/post.php?id=2510][u]left4dead + Plugins Google Sketchup thx RYO http://archlife.skynetblogs.be
You must have this curious violent game (I am not gamer)
But seems you are not obliged to take some weapons
So some ideas can be investigated :)