Yeah I went down this road some time ago, the smallest microwave I could find, tucked into a cabinet, was my best option... Even the professional type towel warmer is not really conducive to what we do, they are more for a shop or as some of you have said a Japanese resturant... They turn then on in the morning and turn them off at closing time, keeping the towels warm all day long..... Same problem with the crock pot idea, which does work by the way just takes forever to warm up... I didn't think of using the steamer idea which we actually have a nice large one, but I do know for a fact the it takes about 22 min to cook rice so if you had the time that might be an option....
If you go with a Microwave make sure you get the rotating type, it gets the towel way more evenly heated.. I never even use my high setting either, have had not one problem since I put one in, other than the wife thinking I have gone slightly over the top with the "Shave Den"