Okay, this is silly, but the original problem was that I got this scratching thing for the cats that has a rope loop at the top to hang it off of something. It's integrated into the panel. I wanted to hang it off of a doorknob, but it's way too long for that. Obviously, I could just cut and resplice (and the resplicing would actually be pretty simple considering it's a non-braided sisal rope) but I just had this notion that there had to be a permanent sheepshank. I guess there is -- the sheepshank plus a half hitch at each end, which I haven't tried yet -- but the point I was missing is that even a sheepshank is really two knots each holding the end of the additional rope. The rope is pretty thick in comparison to its length, so I was trying to minimize the knots used, especially since I was trying to keep the shortening away from the middle so that I could have a single rope thickness over the doorknob. (A butterfly knot worked really well for that.) Oh, and the wife wanted to avoid a free loop because she thought the cats might end up hanging themselves.

I guess it just became more of a curiosity than something that needed a real practical application.