Just relocate it to the inside. I know you can't use a hammer but you can "draw" it into place. Get a couple of allen head bolts (LHS) in a size to match the T-nuts and long enough to reach thru the plywood. 1/2 or 3/4 inch long should be fine. Put a washer on the screw (also try to get a larger washer to spread the pressure out) and thread it into the T-nut. The bolt head should now be outside the fuselage. Tighten down the screw and as you do it should seat the T-nut in place. Apply a tad of epoxy around the T-nut to retain it but make sure to keep it off the threads. Let epoxy set and remove the screws. DONE!