Might have to rig a yolk-type system like the old Blanik L-13 yolk, but installed on the tug end. Model it using a toy Piper Pawnee; tie a string around the outboard strut wing attachment points on both sides (close enough to the CG). Tie the two strings together with a ring in a "Y" well beyond the tail feathers. Attach the tow rope to the ring and voila! If the glider climbs above the Pawnee, the yolk just pivots through the CG, avoiding a tail pull-up.

I thought through the hard stuff, you solve the little details.