Here are some pictures and/or drawings of planing clamps from various makers. If the name of the submitter is underlined, you can go to the submitter’s web site. If you click on the picture of the planing clamps, you will go to a page that will give more explanation of the planing clamps.
Here is a pic of a planing clamp I am trying. It is an "edge clamp" used for gluing veneer or laminates. I elevate my planing forms on a couple of 2 by's and this allows the edge clamp to be used. They are fairly inexpensive and easily attached.
Ron Larsen’s Planing Clamp
I needed a clamp to plane 6' strips for a one piece spinning rod. I bent up a "U" shaped bracket, drilled two holes in the legs slightly larger than the pins on my form & tapped a 1/4-20 hole in the top. I turned the slot off of a plastic screw, screwed it in the bracket & screwed on a knurled knob with a set screw to lock it in place.
I holds quite well, even when I'm using a scraper.