I found some old Fernco (brand) couplings for plumbing repairs in the shop and it looked like they would work. As it turns out, the couplings work almost perfectly. Here is an unmodified end cap. (They also make end-to-end couplings which would possibly provide two connectors.)
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I cut off the end of the cap to make a ring. There were two beads on the inside of the ring, I trimmed one off with a sharp knife, the other fits into the MP-E's mounting groove making the connector even more secure!
The 2" nominal size (also marked 56 - 79 mm on the band) Fernco fits perfectly onto the MP-E which has an exterior diameter of 63mm. The band clamp can be tightened with a screwdriver, nut driver, or a coin. Holes can be drilled in the band to mount lighting gear but for now I'm just clamping things on with the band itself.
Best of all, the clamp provides a shock-resistant stainless steel protector for the end of the lens for those of us who tend to stick the end of the lens in the mud/dirt/gravel, etc. a lot