Sorry, got sidetracked.
Just make a little strip of steel and inlet it edgewise (it ain't comin' back out) into the stock, and make your spring catch on that instead of a buttplate. For that, I don't have a photo. I do believe that the "Edward Marshall" rifle has a piece of metal like this, and the spring catch has two notches, so it catches both on the buttplate and the metal piece.