I have been using this method for 20 years. Cut your melamine/conti board to required size. Screw black painted 1/2 inch square battens to 2 edges, making sure angle is exactly 90 degrees. Trace edges of required paper sizes using permanent marker pen. Spray surface with 3M Spraymount. Compose image using guidelines. Place paper, press flat with edge of hand, expose. The paper is easily lifted of by sliding finger nail under edge of paper. There is no residue left on back of paper. When stickiness is no longer sufficient to keep paper flat, re-apply spraymount. When sticky surface gets a bit grubby, clean with White Spirit (turps substitute) and start again. I have Focomat 11c; the standard thicknesses of Melamine board (in UK anyway) don't match the exact thicknesses needed for autofocus to work, so I have built up the back with 1mm card to required thickness. Admittedly I only use RC paper, but see no reason why this should not work for FB, given that no discernable adhesive transfers to the paper, at least using RC. See photos.