I saw a sewing pony used in a leather factory... Essentially a very specialized type of wood jaw clamp vaguely similar to a screw clamp but with "c"jaws rather than parallel jaws... I don't need a sewing pony per se, but it has inspired me on a potential idea for the jaw design I need. And I can integrate it into the work surface. Machinists have clamping systems for holding work for milling and other operations, and typically the foundation for these systems is integrated into the table. For CNC you build a table with a grid of threaded inserts in your spoil board. If I use one of my thick rubber pads as a spoilboard-like surface, I can have an underlying array of threaded holes in the steel table underneath, and then create an assortment of bolts padded in rubber tubing as well as padded wooden "machinist clamps". Sort of how we use a morton table to set up glass cuts, with pegs and stops, but in the style of a spoilboard grid.
In case you don't know what machinist clamps are or a spoilboard, here is a video
https://www.youtube.com/watch?v=bpJyqLoqV04 of a CNC guy demonstrating machinist clamps on a CNC spoilboard, but he goes on to show some other clamps he is developing. The point is that a machinist clamp is like a one-arm screw clamp, using the table as the other arm. And for all practical purposes this is a milling operation, but we are machining glass, so a machinists style of clamping is appropriate but needs to be adapted to the glass. In the video he does not show any overhead type clamps because in CNC, you can't have things projecting over the work. However we are not doing CNC, opening up additional types of machinist clamps that are possible.
I don't think I'm going to build a grid of tapped holes, but I will probably have a strategic set of holes I add one at a time for each piece I work, until I no longer need to add them. To start with I think I'll just use a sheet of 3/4" marine grade plywood, and use wood screws for the clamping force so no tapped holes or extra advanced work is needed, and after I use that a while I will either love it or hate it, and I will evolve the idea from there. For pegs, I'll get some thick rubber tubing, and some copper tubing, and make rubber coated 2" pegs I can run a wood screw through. By the time the plywood is affected by water damage or screw-hole wear, I will know if it was a good idea or not. I have a large supply of the rubber mats, so wear and tear on those won't be a problem, but they will probably last longer than the plywood. For long-armed clamping arms, I will cut those out of hardwood, I have some oak that would be good for that. Instead of acme threaded rods, I will use lag bolts, as those come in long enough lengths, I'll just have to pre-drill pilot holes for those.
Thanks for the brainstorming help, solutions and ideas always come faster when bouncing and sharing ideas. But I'm actually thinking the CNC spoilboard with half-clamps and pegs is what I was looking for, when I put it into practice I'll post some images... Time for a curbside order from The Home Depot!