My skyripper motors had instructions to put masking tape between the end of the case and the slot, then start at the end of the ring and roll it over the case to the slot. The tape was just to prevent scratching the case.
1. Wrap electrical tape around the small web between the groove and the end of the case.
2. Start one end of the spiral ring in the groove. Push the ring into the groove as you go around the case until you get about 60 degrees or so remaining. Do your best to keep the loose end away from the case, that's really the only thing that will scratch your case.
3. For the final 60 degrees, grab the end of the ring with a pair of needle nose pliers and pull it away from the case. Continue to press the ring into the groove while being careful to keep the loose end from gouging the case. Continue until the nose of the pliers hits the ring portion in the groove. Press the remaining ring into the groove, and remove tape.