A large sheet of plexiglass (or other ridged sheet good), pain into into the developing tray, with chemical, which rest on it when allowed, but otherwise floats above the bottom, could also use rust proofed bankers 's clips at the far, wide paper 's margin, could keep paper flat, for thin or exlarge sheets or transferring to other trays, or a 'waterfall' washing setup, even an archival washer tank, might serve some well.
I have some large trays, but a small space in which to work, so I might give this a try,maybe, but I'll bet tears wrinkles and folds would be a rare thing!