Are you using the metal graflex lensboard? I use plastic, harvested from anything that is opaque and flat. Flat black ABS sheeting is perfect, hobby-grade plywood from the hobby shop would even work if you had a few tools.
I take the plastic and a metal lensboard without lens, trace an outline onto the plastic. Then I take my trusty dremel and just grind out the board.
Then I bevel the top and bottom edges where the sliding lensboard lock would cover, sort of like /--------LENS-------\
if that makes any sense. I've held lenses in with those adjustable plumbing straps that you tighten with a screw, duct tape, epoxy, you name it.
If you get the lens hole a bit snug, usually you can just screw the lens into the hole and it won't budge. Heck, hot glue would probably hold it in and it would be reversible.
I know it sounds sloppy (it certainly can be) but it works. It works well enough for me that most of my lenses are mounted like this.