I use 2 solo cups. Fill 1 half way with hot tap water, put the mouse(in a sealed baggie) in that cup. Then take the other cup and fill it about half way with hot water too and put it in the first cup to submerge the mouse. Just make sure not to fill either cup too high or it'll overflow on you. Let it sit for about 15 minutes and you should have a nice hot mouse. Feed your snake right away while the thawed mouse is warm.

Not sure how you'd do it in a timely manner with more than 2 or 3 snakes though. I guess a big bucket lol.