I have been very successful switching all my pythons to F/T. I thaw them out in a bag submerged in hot water for 30-60 minutes depending on size, then I put them under my heat lamp until they are over 100 degrees F, then immediately feed. Works fantastic.
One time I forgot the rat under the heat lamp while I was doing stuff, and the rat "cooked" and smelled funny. The snake wouldn't eat it, and I have heard that you should never feed "cooked" food to them. I threw it out, and I never leave it under the lamp for more than 5-10 minutes now.