I like cxwrench's solution. But if the cable fails at the shifter end or the cable is simply too frayed to be run into the RD, that's not going to work. (Well maybe if you brought a shop quality cable cutter.) I remember the old SunTours where I always managed to screw the limit screw in far enough to nearly center the RD over the freewheel. That always seemed to me something that should be a design requirement but I'm guessing that has gone by the wayside. The tie-off at the WB cage, now that I like. Do that with the barrel adjust at the RD screwed all the way in and the cable pulled tight to the desired cog. Back out the barrel adjust as your "knot" tightens and settles in.