I just remembered having seen these pass through eBay a few months ago. The pair sold for $27.
http://i2.ebayimg.com/
They appear to have been a response to the lack of quick release mechanisms on Mafac's standard front and rear frame mounted cable housing stops / hangers. I never found that a concern with "most" of Mafac's calipers, but these seem to have been a simple and clever option.
I had never seen these before. Has anyone else ever seen or used them?
Bob Hanson, Albuquerque, New Mexico, USA