I have an osage English long bow that's just come off the tillering tree.  I put a long string on it and it was only braced about an inch but when I gave it a little tug I could feel the limbs fighting each other, each trying to torque the string opposite directions.  Anyway, I know heat and twisting will take care of it but I can't find anything that will grip the flat back and round belly without crushing it.  Any ideas?

Maybe strap wrench?  household model that is a modification to what was used for oil filters.  Sears has them.  Do a search.

Hi Ursus,
Use flat pieces of wood with wood clamps.
For the round belly I had used a section of an old bicycle tire as a protector. The wood clamp handle can be used as a lever to untwist the limbs

F-Manny