I haven't tried this often, and I don't think I have been successful, apart from planting a "seed" or two, but I present facts which actually call into doubt much of the JW teaching or mindset, but I present them as interesting gobbits of information, not in any particular context that the JW will find confrontational.
For example, an Elder was talking to me about all the JW's he knows with health problems, and he said it went all the way back to Adam. I replied "Well I think it surely goes back further than that, Neanderthals had diseases like the ones we have, all of us carry Neanderthal genes, they are to blame for some of our ailments".
This was met with stony silence, needless to say, but if he seeks to prove my, admittedly not terribly scientific statement, wrong, he will come upon some interesting facts !