Hey man,
I just recently went though the exact same experience, took about two weeks of no feed before my lil guy Shrike switched over to F/T. One of the tricks that helped me was "pre-scenting". I fed him in a different enclosure so what I would do is heat up the rat then rub it around the other enclosure for a bit, get the scent going. Place him in there, make sure he was flicking that little tongue out then show him the rat. He feeds INSTANTLY when I do this.
Good luck, feel free to PM me if you have any other questions.
Cheers,
Fatal