I have had some similar problems with my in-laws. I can tell you that deliberately planting seeds of doubt is unlikely to work. You are merely antagonizing them and setting their apostate alarms off. In which case, they won't listen to you anyway. But I can totally relate to getting irritated with the child-like praise. Especially when it seems like they're just saying it to take a poke at you.
There have been times when I finally spoke up if they kept making comments like that. Not to plant a seed, but to stand up for my decision to leave the WTS and to point out that they don't always have all the facts. Also, it helped not feel like I was being walked on. Usually, the response was something like, "Those are just lies spread by apostates." Or, "They just make up stuff like that because they're jealous."
It was really hard not to laugh when I heard stuff like that. They're just evasions, though. They always turned away from me whenever they said them. I usually didn't push any harder than that; it was enough that they knew I wasn't on the same page. Any more and they would have seen me as the enemy.
Basically, people need to be ready to leave the WTS. The more you push them, the deeper they'll sink into the WTS's protective cocoon. And the further from you they will slink. It tends to have the opposite effect of the one you want. I would suggest that it's enough that they know you see things differently and that they understand you have decent reasons for it.