Mine all go in a tea mug (the snakes have their own special mug) with hot water poured on them. By the time I'm done weighing the snakes and getting them in their feeding bins, the mice are thawed and warm to touch. Only one of mine waits for the mice to cool to room temperature...the others prefer them on the warmer side (we've had to warm them under hot tap water if they cool too much)
But, as I've seen from a lot of reading here, different temperament snakes like different things, so if you've found what yours like, that's the important part