Kind of hard to understand the post above but I would not microwave the rat. If you're microwaving the water to warm it up, fine, but even thawing in very hot water is not recommended. At the most, use water that is as hot as your sink will make it.
I have had good luck switching snakes to F/T by feeding them a very small live meal and then a few minutes after they finish swallowing it, offer the F/T. They kind of go into a feeding frenzy when they eat something so small and will take the second meal without thinking about it a lot of the time. You can also try putting the snake in a smaller environment for a while before offering. A lot of times they don't take F/T because they are nervous with the tub open and you standing there etc. If you put them in a smaller habitat they will feel more secure and take the meal. Please note that I'm not saying to use a foreign feeding tub, but rather to house the snake full time in a smaller tub and then try offering there after they are used to it.
GL