How should I restore braze-on brake cable housing guides?
A long time ago I used some clamp on cable housing guides on a frame &amp; I didn't have any issues with them moving.  I did have a slightly larger cable housing  with teflon sleeves inside, so that the clamps could be screwed down fairly tightly and still allow for easy movement of the cable inside.  You might want to see if you can get perhaps another brand of clamp.  From memory I had some Gran-Compe by DiaCompe.  Alternatively you could try putting a thin rubber shim around the clamp to get it to grip to the frame better.

The only other alternative I would consider would be to get a local framebuilder to remove the old guides and braze on the new ones.  I don't think it will be that pricey.  My old LBS used to do this sort of work once a week, and a job like that would only have taken about 10 minutes to do.