Okay it's not the most hi-tech device ever, but it does work very well. In most cases it will decurl a piece in 20 minutes or so.
It is made from a piece of mat board as the base. A sheet of mylar is attached to it at the end with the tape of your choice. Finally, the other end of the mylar sheet is attached and wrapped around a 2 inch card roll and a piece of duct tape secures the sides of the mylar to the roll. The back-stop keeps the whole thing from unravelling.
When a print is placed into this contraption, a spring clip holds the roll from moving.