Make a small plate with a hole and an 8mm nut welded to it. Thread a piece of strong curtain type cord through the hole in the body, and pull it through. Then thread the end of the cord through the nut, and tie a knot on the back to hold it. then use a small amount of PU sealer, on the side of the plate that will be up against the inner panel when you pull the cord back the other way, which will put the plate in the correct position, leave the cord tied to something to maintain the tension while the sealer sets
Leave the sealer to set for about an hour or so, before cutting the cord, and letting the knot drop away...
You should then be able to carefully replace the ball joint back in, and tighten fully
I would also recommend that that you change both struts, as they could be starting to seize up, causing excessive fatigue on the body, causing the problem in the first place
HTH
Thom