Since he isn't knee-deep in the religion and just happens to believe they're right, maybe discussing it with him wouldn't make him explode. (Talking to a true-blue JW usually isn't productive) It sounds like you've already had discussions, though. Have you ever gotten him to discuss a doctrine with you all the way through?
They are definitely trained to shift around and avoid getting pegged down. When one argument starts to look weak, they move on to another one, all the while believing they still have the weak one as a "point". It's maddening!
When I tried it with my father-in-law (a "ministerial servant" -- like a deacon) I thought we could calmly go over the subject of birthdays. That discussion resulted in a document describing why the Watchtower forbids them, and why their arguments for it aren't sound. (You can read it at http://thebentinel.com/jw-birthdays.html)
I went through them with him, point by point. I kept him on one argument at a time, and discussed each one to the point where he had to concede that the argument was undefendable. We did this through all of them, maybe 8 separate lines of reasoning. He couldn't support ANY of their arguments, but in the end he still maintained that all of the arguments "taken as a whole" prove the point.
How do you argue with that? :-(
Lot's of good stuff on this site. I hope you're able to free him from the guilt, that's some nasty stuff. And so unnecessary!
Have you and/or he read Crisis of Conscience? It's written by Ray Franz, a former Governing Body member (the top brass of the Watchtower) and it is major eye-opener.