[DonRotolo]

Preventing the clamp from rotating on the horizontal bar would be very difficult in my opinion. Especially without damaging the finish of the bar.

Here is a different idea: what if your clamp were to clamp onto the bar and the robot were to spin sideways, in the plane of the pyramid's face? If the clamp were several inches wide and had a soft grippy foam surface, it might not spin around The axis but lift the robot into the air, kind of like what team 33 did in 2010 breakaway.