Something that I have tried and I have had great success with, and it works with switching from live to FT as well as mice to rats.
If I am trying to get the snake to eat FT I offer the snake a very small food item(off tongs). Say the snake useually takes a large mouse, I would feed it a hopper. The meal is small and not satisfying. The snake will still have a feeding response, so after the snake has gotten the hopper down, I offer a FT small mouse(off tongs). Try that a few feedings and then only offer FT. I have had great success this way with switching to rats also. Offer a hopper mouse followed by an appropriate sized rat. I would say I have close to a 100% success rate!
Hope this helps.
Happy Holidays
Shawn Turnage
www.twistedconstrictors.com