Like they ^^^ all said.
I also nuke mine and it comes out good if you take your time for smaller amounts. Heat-stir-heat-stir and repeat every minute, or what I usually do is put the already thawed meat on the defrost cycle. Heats it up slowly and my microwave makes me check it every so often. Then you can flip it, stir it, or whatever so that it heats evenly and you don't overcook the outside stuff.
With 2 butts worth, I'd probably go with a pan with your favorite juice and a bit of water, cover and put in the oven low. And stir every so often.