I think it was this site that suggested using duct tape. I took two pieces of silver duct tape, stuck the shorter piece inside the middle of the longer piece—sticky-side to sticky-side—wrapped two of these around the boom, and never looked back.
Sailors will want to make the size large enough to thread the mainsheet through them, long enough to assure that the duct tape sticks to itself (on the boom), and "mount" them away from the sail rings. No shopping required. Residue can be removed with Goo-Gone or WD-40.