theres always the concept of just continuing to buy 12x20 film (imagine the money savings would be minimal over custom 10x20 film getting cut) then you could get an extra darkslide and create a "mask" to slide into the holder that would mask the 1" off the top and bottom, you could even black out your GG to only give you the 10x20 area. just an idea. Kinda like using an extra darkslide to shoot 4x10 on 8x10.