The center post on the clutch is hardened steel. It can be removed, and welded to a common steel pulley. A spacer behind it made of the same hardened steel will allow you to set the offset. Your Boss is a template for another spacer, and the splined drive face is the "stay for the frony. Weld the drive face to another pulley, and there you have it. This is a dirrect drive set up but a longer belt, and an idler pulley can be used to act as a lever to allow slip. This is how "salt flats" scoots are set up. This link shows one with a clutch. More complex but the same idea...
I think you'll see why I am heading towards a HGT Aprilia!