Damn it, its been so long since we had a religious thread in the wrong place, now I have to listen to all these "I never associate with religious people" and "Its impossible to reason with them", *sigh*. Honestly though I can't think of a single time in which I had to reason with them, no one I ever met thought homosexuality was wrong, or evolution, and I haven't heard an argument against any thing like birth control in a long time.
In your case though your just trying to prove a clearly evil group evil, so simple go thorough a list of things that Westbro has protested. Do you hate; solders, americans, gays, musicians, comic book nerds etc. If he admits not hating even one of those things tell him he's going to hell for being a symphasizer. Westbro disregards many off the basic Christian believes such as forgiveness and loving they neighbor, he should realize that they only share a book. If not he is clearly stupid, not much you can do about that.