Personally, I think the key to any feeding problem (aside from an emaciated snake) is starving. The hungrier a bp is, the less picky it is. My male pastel was a picky mouse feeder when I first got him. So, I starved him out a bit the last few months, not completely but just feeding him less often than otherwise. It was more to improve his feeding response rather than to switch him to rats, but the last few times he was taking mice so eagerly I offered him a rat just for the heck of it and he took it right away.

I had a hatchling that was the same story; fed him less often and he's started to take rats no problem.