The book "captive of a concept" has a very good suggestion. It suggests that you become the student, the only way that a JW will see you anyway, and that you ask him appropriate questions that will slowly undermine his beliefs. This will take a long time though and you will have to look into the beliefs yourself and know what he is going to say next. A very good site to get the low down on JW's is Jwfacts.
No guarantee that this will work though. JW's belong to a cult. Not the best odds to fight against....
Let us know how you get on…..
Mr.M