I wanted to use larger, 2mm glass plates and thought a solution might be whole-plate holders from much much older cameras. So I have built myself and adapter back for my Intrepid 8x10 and it appears to work. I've never seen this done before and thought people might be interested.
Thanks. I'm actually making my own silver gelatine dry plates (1880's style) and want to be able to carry half a dozen of them. If I were doing wet plate (1850's style) I'd probable stick to a regular film holder with the septum cut out the middle as you only need one and it only holds the plate for a few minutes. Wet plate is an easier problem to solve in that sense.