Here's another idea that would give you what you're looking for, and your 80/20 bench would allow for a solid attachment. Drill two holes through one of the jaws of a large hand screw and bolt it to the bench top extrusion, it would work in the same fashion as the shaving pony, but take up less storage space - a big plus in a small shop - when you're not using it. They make some pretty large hand screws, but it would be easy enough to buy the hardware and a couple of chunks of hard maple and make your own if you needed longer jaws or something custom. Plenty of articles out there on making your own, dead easy if you start out with the correct hardware.