RE: Is there a quick fix for this?
Tip for installing new blind nuts in an inaccesible spot. Get some threaded rod and poke it through from the front.
Wind on the blind nut with some 30 minute epoxy [ 5 minute is ok if you work fast ]
Pull the studding out until the nut is up against the back of the firewall, wind on a washer and nut from the front and use them to pull the blind nut up tight.