I love to do this with left a left over prime rib!
Well, they aren't exactly store bought, but isn't that why you make stuff at home? The mashed potato consistency really doesn't turn me off, but I am going get some shredded hashbrowns and try it that way. The biggest issue will be the ability to bind it all together...also, you would need to blanch raw potatoes to get a jump start on cooking them...
As for rolling long cylinders, I tried that at first and it will work. I rolled it in parchment paper, but it's just as fast to shape them with your hands like you would sushi rice. I have a small fry daddy and they turned out pretty good.
I also ground up some bacon in a meat grinder and added that to the mix, along with some granulated onion and garlic...good stuff!