Even more importantly if someone had asked me who from my former indoctrinated friends i would consider least likely to defect, I would answer him.
Many would have considered me in that "least likely to defect" category. But my defection came at my own time and pace. With being a JW, it's not just about opening up to doubts, it's realizing all the consequences that come with opening up to TTATT.
If he's not really ready for that, the best you can do for him is be a good example. Be a happy, healthy, and productive member of the human family, and not a bitter, angry, or argumentative "apostate". Give him plenty of space and time, it's not like an "exJW armageddon" is coming tomorrow and he'll be destroyed if he's still in the cult.