From the back mark the bellows opening. Remove the material outside of the bellows opening mark leaving a 1/16 - 3/32 thick lip between the bellows opening and outer edge of the board so that the board just sits into the front standard and the board locks just slide over the board.
This is the part that I'd assumed wasn't feasible---getting that thin lip between the standard and the locks, without thinning the wood so much that it's a break waiting to happen. But if there's that much clearance...I've pointed my captive woodworker at this thread and I'll see what she says. She has a mess of thinstock available in interesting woods and historically has done a fine job on Eastman 2-D lensboards with it.
San Diego, CA, USA
The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
-The Little Technical Library, _Developing, Printing, And Enlarging_