Well, good news on the screen plate front. After first receiving a Linhof Pressure-Plate Film & Plate holder, I've now got two sheets of 0.55mm glass that beautifully sandwich two sheets of film together.
The whole setup is so effortless I'm kicking myself for not doing this earlier. That being said, I've yet to take any pictures, but it appears absolutely flush and there'll be no more messing around with ridiculous schemes that involve coatings or adhesives. Woohoo!
To commemorate this moment, here is a synopsis of pages 86 to 87 in J.S. Friedman's History of Color Photography, edited for dramatic effect:
To offset the possible effects of poor contact between the various members of the [sandwich], J.H. Smith coated the emulsions directly one on top of other, but with an insulating layer of collodion between them... Biehler accomplishes the same result by coating intermediate layers of soluble cellulose esters between the emulsions layers... The Gevaert Company would separate the emulsions layers by means of paraffin.... Rowland S. Potter placed a thin transparent adhesive consisting of a soap solutions... L. von Tolnay and L. von Kovodsnay applied a vacuum to bring the members into close contact. EA. Weaver would put a mild adhesive between the elements, the adhesive containing at least 60 percent glycerin... W.H. Moyse claimed to have obtained better contact by the mere expedient of surface coating the emulsion layers with a colloid... But the problem of good optical contact can be solved most easily by the use of pressure plates.. The three elements are placed between two pieces of glass of appropriate thickness, which is determined by mechanical requirements. The sandwich is then loaded into the plateholder, the back of which has heavy springs which exert considerable uniform pressure upon the glass plates. This simplest of all devices proved eminently successful and altogether sufficient to overcome any flaws that might be due to poor contact.