Olympus makes wrist lanyards where the cinch cord is very much like wire. Using the method you showed it can cinch onto the clip a bit more positive. If I recal correct I found some at Amazon for $5(?).
What you did should work. Perhaps a wrap of tape (or rubber band) around the cinch point would keep it from sliding forward. Or your o'ring idea is fine.
I drilled a 1/8" hole in the shoulder of a tailcap on mine. Using an enamel paint pen masked the exposed alluminum. On my EDCL2-T I drilled a hole through the clip.
Realizing that's not your desire, I'm just tossing it out there.