Easy 1-step Instructable: This is a very simple padding solution for 3/4" pipe clamps that requires no drilling in the clamps and no gluing. The pads double up as stands for the pipe clamps too. They can be made in a few minutes with scraps of 1/2" plywood and are secured using cable ties. The groove is done on the router table and is a few millimeters deep.
I drilled the hole with a 35 mm Fostner bit used to install European style hinges. Those bits are very commonly available.
I made a sketch with the dimensions I used, but do check first with your own clamps if you decide to make this.