If they are the original boxes held to the studs by nails, I've had
good luck by; pulling the outlet out of box enough to slip an extended
driver tip past it and tag it down with a 1 5/8 drywall screw. It will
be at a pretty steep angle, but will suck it back just fine. Also a
good practice for ceiling boxes when you want to hang a fan, assuming
there is anything to screw into.