That is exactly what I am going to try this weekend, only I'm going to use a small cooler instead of a bucket.
The thing I found with microwaving my mash is that unless the container is insulated, the temperature in the mash isn't very even. As a matter of fact its cold at the top, bottom and the sides. So I recommend using an insulated cooler.
I'm using an old steam kettle. I'm feeding the steam in from the top instead of underneath the false bottom. There are some dynamics with the steam interacting with the water that might be in the line feeding it. I think I'll need some sort of a checkvalve so that the steam is released right at the bottom of the vessel. As soon as the steam hits water it going to release the heat and you have to make sure that doesn't happen in the line. Or maybe the steam has to be volumous enough that it pushes the wort out of the feed line. It will take some playing around to get it right.
Keep us informed. I'll write up my experiment when its done. Right now I can't find a cooler !