I think you'll get better results from the previous posters, but in case you get in a bind, I thought I'd tell you about my recent experience. I cooked up a bunch of baby backs (half racks) and wrapped them in butcher paper for the final hour or two of cooking. Pulled them all off, let them cool down for about an hour, then put them in ziplocks to go in the fridge. For several days afterward, I'd pull out a half-rack (still wrapped in paper) and put it in the microwave, for maybe a minute or two (watch them closely). The butcher paper keeps them more moist, and the results are good (I mean, they won't be the best ribs you've ever eaten, but your friends will be seriously impressed). I got the best results by leaning two half racks against each other and microwaving them that way.