Folks have had success with that method. If you can successfully get them going on P/K, you might want to take a laser temp reading of the rat, and try to achieve the same when you present F/T.
Thomas "Slim" Whitman
Never Met A Ball Python I Didn't Like
I tried frozen twice first time she really did care or seem to have any interest in it so I laid it next to her and she finally ate it after 20 mins or so. Second time she didn't care at all and after a few hours I threw it away. Reason I'm thinking the prekilled might help is that I've noticed the f/t versus live have a noticeable difference in smell. I stick the brown bag in her cage and within seconds she's out of her hide ready to strike. Stick a F/t heated to the same temp as live in there and she'll just stay in the hide.