That the frame is steel changes what I would do to repair the cable stop. And looking at the photo more closely changes my speculation as to the cause or the failure.

Being able to, I would remove the bits of the old stop and braze on a new one. This would damage about 6"+ of paint. For the short term I'd rattle can a touch up but would plan on a complete respray in time. I would also consider how I'd want the braze ons elsewhere be different given the complete refinishing.

My suggestion to have CoMotion involved if possible is still the first step and I would only do it myself if they were of no help. Andy.