There are insertion type roll holders that slip into a spring back like a cut film holder. Makes and models include:
Calumet/Cambo C2, C2n -- these are made by Cambo, 6x7 are more common than 6x9
Sinar -- a variety of models, most long out of production. Some multi-format, some ("Panorama") fixed format. I have a 6x12 Panorama. It is a tight fit in a 4x5 Cambo back.
Toyo -- several models. These are 48 mm thick, won't fit all spring backs
Adapt-A-Roll 620 -- these were made in three sizes, to fit 2x3, 3x4 and 4x5 cameras with spring backs. All have 2x3 (6x9 in metric) gates. I use 2x3ers in my 2x3 Graphics, have had a 3x4, and have a 4x5 for my 4x5 Cambo. They'll feed from a 120 spool but must take up on a 620 spool. The 4x5er's gate is offset from the center of the camera's gate, I marked my gg accordingly and know how much rear shift to use to center the roll holder on the unshifted front standard.