I absolutely struggle with it as well. No matter how hard I screen at interview. I find that the kids who DO play, play limited versions of TV shows. They also need a TON of attention when doing so. "LOOK AT ME. I AM _______!!"
I do a LOT of modeling play. A LOT. Then I step back, watch how it goes and intervene when they start to leave to get them reinterested. I have had moderate success with a few of my kids. The rest, even after months and months----nothing.