I think a lot of people put meat in a ziploc bag and then put the bag in warm water. This will increase the temp of the mouse without cooking it...or you could put the bag under your underarms... =) that might work too.
You just thaw them, LOL. I divide a bag of 50 into 10 bags of 5 each. Those go in the freezer. On nights when I plan to feed mice in the a.m. I take out a baggie and toss it in the turned-off oven overnight to thaw.
You CAN feed them straight out of the fridge, though, too. They don't have to be room temp any more than any other meat does. Just can't be frozen.