Paul Monachino used to give a class demonstrating how they can be made. He hung around M&H as a kid after Aeolian took it over, but while the old techs were still working there. As they retired them gave him their jigs. Each person had to make their own jigs back then.
It was ingenious but not that difficult to do. You'd need to get the right density of bass damper felt, and to make the jigs. Someone probably still knows how to do it.
My sadly vague memory is that the various jigs held firm and supported the parts of the bichord damper which weren't being cut so they couldn't squirm out of the way. Paul had an extremely sharp knife which he touched up frequently.
It would cut one of the four needed faces, then the damper could be reversed in the jig or put in another jig, and he could cut one of the others. The cuts were straight, so the grooves for the two halves of the bichord started as v-shaped. Being installed turned them to the curved shapes, just like monochord dampers.
Also, it was only the bottom part of the bichord section which has these "double-bump" dampers. They are for the larger sizes of bichords.
I have a vague memory of someone in Colorado having learned the procedure and made some jigs? A source for the firm bass damper felt was needed.