I don't think handles for these are real complicated. I've always just grabbed my 1/2" ratchet and an extension and, for the small amount of turning I had to do, even doing dowels, that method worked fine.
I just went out to the shop and peeked. If you want a crank handle, it may be no more complicated than grabbing a five inch long, two inch wide piece of 3/4" ply, putting a handle near the end of one side and a 1/2" socket extension on the other side, at the end opposite the handle (again, near the edge).
Attaching the socket extension would be the most complicated thing, but could be as simple as drilling a hole the same diameter as the female end of the extension, then taping it into it.
The extension could be held in place by drilling holes that would allow you to run screws through the extension walls of the female end, so they'd go into the plywood.
Lot of choices open to you.
The reason I have what you want is, I never lent it out before.
Scraps are a myth.