From what I remember, working in a photo store in the late 60's: I met a guy named Carl Ness, in the Wash DC area, who invented, and at the time was manufacturing the "Carlwen" neg carrier (I think named for him and his wife-Wendy?) It was a sliding flat holder with 5-6 apertures spaced like film exposures. It slid, very smoothly (it was well made as I recall), in a carrier, which mounted in the enlarger like a normal carrier. You could move from one image to the other without removing the whole thing, kind of like Beseler's negatrans, which came soon after, but with a different design.
I believe the film was immersed, or coated, in silicon, I never knew why, but your post reminds me of it. I don't know why I remember all this, nor how accurate it is, but I'm pretty sure. (This is where I would put in the winking face - where do you guys get those?)