Standalone 

fear not, old's cool! Here's my solution with the same rack:



And some thumbnails of the details:

The first two are an attempt to show the metal piece that I bent into shape as an attachment point for the brake boss. I believe the metal was taken from a trashed 1970's kiddie seat rack. It took a bunch of trial and error and rebending. I used some vise grips to do the deed





The rest show how I pulled the brake off and threaded it through the rack. I don't think all sidepulls would work, but old sidepulls are plentiful and I think some trial and error might work.