My rack has a single hole for the standard flat metal bracket supported reflector. I will get a tube of aluminum, put a cap on one end, drill a hole in it. Then, paint it matte black to match the rack. A long screw goes through the rack, tube and it's cap and will be nutted in place. Next, install onto it in the usual pipe mount fittings the Cat-Eye and a reflector. Meanwhile, the light is currently affixed to my Arkel Tail Rider.

That's not a bad idea. You could probably mount it underneath the rack too, so that it is out of the way. That would work better than my film canister idea... Better go to ACE hardware and do some looking around. Instead of a cap, a decent sized washer or two might work well too.