If you have a few extra bucks, find one of those cheap mini-fridges at a yard sale and set it up somewhere. Depending on the temp of the mini fridge, ~24 hours before you feed. At feeding time setup a bowl of warm water to get the body temp up to feeding level.

One of the problems with F/T is putting a full size rat in a bowl of warm water could take hours to thaw it out on the inside (while the exterior may be warm almost immediately).

And seriously, the microwave method can be an ugly, ugly situation if you screw it up and leave it in there too long.