Well, at West Coast Camps, Mike Schweene has one. It is pretty cool. It is weighted on the other end to give you a better feel for handle passes. I will see if I can talk to him and ask him what all he used to make it.
Basically you use two pieces of plywood and make a huge Lazy susan. It's pretty easy. Then you attach a handle with weight through a pulley to simulate the pull of the boat. They are nice, just be careful to keep them away from glass doors. A friend chalked her back up and got stitches from bailing through it. No bueno!