[Jim Jones]

Yesterday I used some honey to glue 18x24 cm film to cardboard, that was put in the plate holder where the glass goes. (Others have reported using jam with success.) Worked fine, except that my 1980-s Tasma film seems to be fogged. (If I am not still using it backwards...) If you don't get the film to stick to the cardboard/glass whatever you use, it might get trashed by the darkslide.
The prewash washed the honey away just fine...

/matti

That is a sweet solution to an old problem!

Long ago metal septums were available to hold film in plate holders. These were usually made of metal with three edges rolled over to retain the film. They can be improvesed from thin sheet metal and painted black. There will be a slight focus shift, about the thickness of the metal. The typical small apertures one might use with an old plate camera should cover that. The film should be backed with loose cardboard to minimize this. With a little more work, one could adapt 5x7 sheet film to whole plate holders.