If you get plate holders instead of film holders, you can use the exposed plates as backing for the paper. Ole used jam as his adherent, I've used sticky wax (from an old wax-coater used by layout people in the days of dinosaurs). Either way, the paper lies flat on the glass and, though it means that the focal plane is advanced a few thousands of an inch, I don't think it will make a difference. It's an easy way to get started without buying more gear.