I suppose it might have to come to that someday when all the old wood holders are gone. I tried with the Lisco/Fidelity version. They. at least, have what looks like a seam. I still managed to shatter the plastic trying to get the halves apart. The Riteway holders don't even have seams. The plastic Riteways look a lot like wood. Could be what you saw (??). I think it might be possible for a metalworker with the right tools to cut the septum out, leaving the plastic frame intact, but hopefully, new plate holders will be available before the cheap, old wood film holders are gone.

Randy, You mentioned being on a budget so I didn't mention that Chamonix cameras is planning on coming out with a couple of plate holders soon. I imagine 4"x5" will be one of the sizes. Bound to be expensive, but also gorgeous. http://www.chamonixviewcamera.com/accessory.html