All I do with my F/T rats (and mice) is get everything out of the freezer a couple hours before feeding time. 10 minutes before feeding put two at a time (in a zip-lock bag) in a large bowl with the hottest tap water I can get. After ten minutes I take them out, roll them up in a paper towel to dry while I walk to their cages to feed. If they are still damp I use a hair dryer for a minute or so.
I get an immediate response as soon as the cage is opened. The snakes are very active as they can smell the rats. Seriously 95% of the time they strike in seconds. And when they haven't hit it the first time, another minute under the hairdryer always does the trick.