Hi Murray Smith,
Maybe have the BBQ, but then ask him to meet just with you, and confide to him, as a friend, that you have "doubts" and would like his help. Pick your doubt carefully, and have it really well researched. My personal favorite is asking for proof that the WT was chosen by Jesus in 1919; would it be reasonable for J to do this and provide no scrap of evidence for "honest-hearted" ( ) non-jws ?
Then use Black Sheep's methods. Don't let him shift the goalposts or answer a related question; act hurt and disappointed if he tries anything like that. Mention being stumbled.
From my experience he'll avoid you like the plague after one meeting; two at the most (he might try to research and/or bring backup, but of course you will only confide in him alone, and his research won't help him).
But when he runs, his doubts will run with him.