This looks like it should do the job. The cable is super heavy duty, 3mm diameter. I couldn't find an appropriate nipple to use so I drilled down the centre of a short M6 allen head and soldered that on as a nipple to go in the clevis.
I wasn't appy with the top cable stop, then I looked at the thing they use on the front brake. I just drilled two holes in a bit of EN1 hex bar, one was tapped for a stud to hold it to the frame, the other tapped for a cable adjuster to allow a little more adjustment before bottoming out the threaded section.
I'll need to grind a bit more off the corner of this cable stop so it doesn't foul the snail cam.
I still need to get a new brake cam fitted (threads are stripped on this one), bed the shoes and give it a road test.
L:ink to short video