some guy once told me that he uses a short piece of a spoke instead of cable to set the rear derailer to a fixed position so that he can have chain tension with verticle dropouts on his single speed. i don't know how to describe it any better, but he basically uses a spoke in the rear derailer where the cable would usually go, which eliminates having to run cable up to a useless shifter to hold tension. has anyone heard of this or know how it's done?