Kodak used to make a product called Photo Flat. It was a coating which was brushed on to a surface and never really dried and was slightly sticky. A long time ago, I saw someone use it to hold film in an old photostat camera. there was a post with a formula on APUG a short while ago and I cannot remember the thread. I wanted the formula myself. When I find it I will PM you the information. It will be a few days before I can search.