Interestingly enough, I bought one of those really crappy rowers at a yard sale, but it has a good sliding seat and foot pads. I got it for $5.00. 2 cheap pulleys and a loading pin later.... I put about 25lbs on it and row away, it forces strict form to keep it from swaying to much. I let you break the ice on the idea though(they're all gonna laugh at me) I like the exer-band idea though, I will give it a try.
I also train grip alot, and I have made about every device for that that you can imagine. If anyone is interested, I will post descriptions and instructions.