I have a couple snakes that'll eat f/t that you just drop in the tub, as long as they smell the rats before I open the tub, but for a snake that doesn't care much for f/t you have to do the dance and entice them a little. I've fed live a few times and I really don't like it, last time the snake hit the butt and basically strangled the wrong half of the rat, so it was alive and screaming the whole time and I stood over it making sure it didn't bite my snake.

If you want to switch him get a scale, weigh him, then watch his weight. Every week try to feed him f/t, if he keeps refusing then watch his weight. If he drops too much then feed him some live, but eventually he'll probably take f/t.