Just duct tape the nut plate to a yardstick and slide it down the stake hole. Pull the yardstick out when the screws are in place. I’ve done this sort of thing many times to secure something to tubing or other places inaccessible on the back side. If you want it to stay in place just smear some epoxy on the surface to retain it in case you need to remove the D-ring mount for any reason.
Mark
