You can just thaw them slowly overnight in the fridge if you want. I put them in zip lock bags, two actually to keep them from getting wet and washing off scent or away anything that should be in there, and put them in hot tap water until they are thawed all the way through and around 100 - 110 degrees. No microwaves or boiling water. I'm sure if you controlled the power and time just right you could use a microwave, but you don't want to cook the rat or anything.
I think I discussed this here somewhere, but I call it the "zombie rat dance". Get it up to body temperature, and hold it in tongs or forceps and wiggle and jerk it around a bit. After they are used to it, most snakes don't require any enticing. Some you don't even have to really warm it up much for, they are fine at room temperature (it should definitely be thawed always.)
