1) They should replace the frame.
2) You can increase the height of the slot, but maybe only 2-4mm.
3) You can run the 50T big ring (perhaps in conjunction with #2).
4) You could TIG an extension plate on (wet towel and icepack the ST).
5) You could carefully remove the outer section of the braze-on, touch up paint, and run a clamp on adaptor at whatever height you like.
Good luck...