Never put anything metal in a microwave. I also would never put anything that goes on my feet inside a place where I heat up my food. Why would you even want to know this? Seriously, put them in a dryer or build a fire outside and put your feet next to it.
If this is a serious question, use the oven Kramer style. I've done it with shirts on cold days when I'm sick, 300* oven on foil and check them every few minutes. I assume there's a risk of shrinking, but it's never happened to me.
The heat came 'round and busted me for smiling on a cloudy day