hey bad boy,
personally, i think there is a really easy way to make a JW think:
put the brakes on any conversation that involves the bible. they consider the bible home turf, so if you pull it out from under them, they are left to discuss the posible existence of God with you, which invariably ends up as an evolution vs creation conversation.
at this point you can talk about science and scientific method. and if you get them interested in science, and scientific method, then they will begin to compare the rigors of science with the way the WTS has treated scientific issues. this is a seed that i know, from experience, easily germinates.
peace!
tetra