The deck plate idea is probably an easier and more elegant fix. You have to fix your deck anyway, so why not install something bigger than 2" (more "wiggle" room), like the Beckson deck plate shown at Deck Plate / Inspection Port
. The downside is that you would need to borrow a 4 1/2" hole saw, but you could install it temporarily (use tape to get a waterproof seal) and let the plywood dry out. You might then seal the cut edge of the plywood with a low viscosity epoxy and caulk the plate for a permanent installation.
Should you forget to remove the plate and crack it, you would simply buy a new one.
P.S. I have no connection with Beckson or Defender.