Well, I made one. And I suppose it is more of an image shaper or formatter for FILM (don't stone me). Lemme essplain.
I took a plastic artist's pallette. Cut a piece to Cokin a specifications. Cut out a slot across the middle of the short axis of the filter that was .302 inches wide and the length of the filter minus about .375 inches on each end. I also painted the side facing the camera as the white material showed up through the viewfinder. It slides into a Cokin "A" style holder and when you look through it, you see an image that is about half of the height of the 4" height of the 4x6 in the viewfinder.
All this does is alter the shape of the image. It was something to play with and I know we could always crop a "panoramic" but this helps as a visual aid and really produces some interesting altered perspectives in the viewfinder. I have yet to click the shutter, but I will today and post some images to my gallery.