Thanks to everyone for the suggestions of uses for a really long narrow warp. Many people said ribbons and trims, and I had the same idea, so I did try weaving a bit of various narrow warp-faced trims. But that got old after about six yards. Plus I kept thinking, the shipment of yarn for sampling for the Very Large Project is on its way; I have to get this off the loom.
So the answer was to pull it off the beam a few yards at a time and make it into cords. Lots and lots of cords, for hours of ply-splitting fun.