Not relevant to the OP, but I just wanted say "Thanks, guys". For brunch this noon I tossed some leftover mashed potatoes I had into my panini grill (which I think has Teflon-coated plates) with some margarine and left them for 10 minutes on medium heat until all the steam escaped. Foolishly, I checked after 3 minutes and the entire project looked like a failure. After 10 minutes, they peeled off into these beautiful, thin, ridged (not rigid), potato cakes. Looks like first-hand evidence that it's moisture in the potatoes that allow them to stick to the pan.
I am going to try this with a stainless steel pan now, just to see if I can get the same trick to work, which I would do with well-wrung hashed browns, since it would be a real trick to remove the moisture from mashed potatoes in a stove top pan.