The only improvement you can have is to clamp the PCB from the top to the bottom (like microscope slides) with a leaf spring type assembly so you don't accidentally bow your PCB if you are tightening it. A screw can put an awful amount of mechanical force on something. I can maybe see it being a problem if you flex your PCB, solder like a BGA or some shit to it, then unflex it. You could bend something out of wires to do the trick ok.
Otherwise I wonder if putting blunt needles in the edges would work better ,since no one cares about the edge of the PCB and they can dig themselves in a bit without as much force, if you can't justify occupying the top with springs.
If you make holes for removable or adjustable needles you can hold irregularly shaped PCBs very well (graphics card, mouse PCB, etc), so long they are not ceramic. I mean like micrometer/screw adjustment for the needle depth. You can cut crude points using a dremel or file.
I would not recommend using needles or a clamp on ceramic PCB however, only carefully distributed top force.