Hah, Kaylee picked it up really fast (it was about dinnertime anyway). I started with a sealed box just so they wouldn't simply flip the mat off the treat. She scratched, I marked and treated for a while, then started naming it. It didn't take long before she was doing it at command. Then I wrapped the box with a towel, gave the command, and she did it. Then she did it for the towel laying on the floor. Quick little beast. I'll have to get an actual doormat and train them more at this-- it's a behavior they enjoy and it's useful! Thanks for the idea!
Sam is catching on too, he is confused at the just-a-towel point so I'll work more on the previous step with him.