Don't tell them anything. Just ask questions
"I know from personal experience that when you leave Jehovah and go out in to the world and do your own thing it always comes back to bite you."
"Just because you can't behave yourself without an Elder leaning over your shoulder does that mean that the rest of mankind suffers your same lack of self control?"
asked me if she had anything to do with me not attending meetings.
Ignore every question you don't like and ask for something like his explanation of the new overlapping generation doctrine. Did Jehovah really give them the previous explanation? Why did Jehovah lie? If He didn't lie and they are spirit directed how did they get it wrong? How is that any different from Harold Camping changing his prediction to invisible after failure? Is Harold Camping spirit directed? How does he know that? etc..
Then stay on your chosen subject and keep him honest.
Every time he answers, ask yourself ...... "Did he really answer the question I asked?" If he didn't, point out his deception technique, tell him you are disappointed that he would try to deceive you in this manner, then ask the question again without rephasing it.
He needs to feel guilty for every sin he commits trying to fool you. Make him pay.