Hopefully someone will come along with more knowledge than I. I have reheated fresh cold turkey meat (60 some whole birds cooked and pulled over a couple of days) in the steamer and then kept them in a lined ice chest for hours and they stayed hot and moist BUT prime rib I don't know. If you do it that way I wouldn't steam them long and I wouldn't do too many at a time but you probably already know that. Good Luck and I hope someone comes along soon with some real knowledge! If all else fails serve a honkin' good gravy over it!
"Life isn't about how to survive the storm, but how to dance in the rain" Unknown