Earlier this year I was in a friend's bike shop, where he deals mainly in used bikes and parts with a bobbish flavor. He had a pair of late 80's or early 90's mountain bike levers, maybe also made by Dia-Compe, with a guidonnet-style bend in them, that had been intended to allow the use of brakes while riding on bar-ends. They were significantly beefier than Guidonnet levers and immediately got me thinking along these lines. Unfortunately I think the clamp was intended for flat bars and would be too wide to fit around the curves of a Choco or Albatross, and the angle of the bend was more acute, to follow bar-ends which generally angled in.
I also think Paul Components, in their early days, made some lever extenders for a similar purpose. Maybe an alternative?