Another option would be to Navajo ply. You end up with essentially a three ply yarn, but since it's sorta like chain plying a single strand (which is what Navajo ply is) you start at one end and just keep going til you get to the other. Also, since it all fit on one bobbin, it will still fit on one bobbin when you get to the other end. Oh, well, is it spun on a wheel or a spindle? Well, either way, one bobbin to bobbin or one spindle to spindle full will be the same either way.