2020 NEC Secured

I think the OP had a wall added to avoid columns. In that case there would be no access to the back side to add anything. He would have had to do it before the drywall went up.
I was thinking that certainly a piece of metal stud could be screwed to the back of the wall stud from the front.
 
One fix might to drill and tap a hole in the box and run a piece of threaded rod in until it hits something
That is an idea. I would have to tap a hole in the box and put some sort of protection over the sharp part of the threaded rod.
 
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