mid-corner is definitely one of the more difficult corner phases to free the car up. especially when the car is a front heavy production sedan with a high cg, roll centers that are all over the map, and a camber curve that blows chunks.
adding more rear spring or bar will have a very minimal affect on mid-corner. it will mostly change the corner entry balance. raising the rear ride height will also mostly affect corner entry.
taking out rear camber will have minimal affect on entry and will free the car up mid-corner, but like tom said, it might make the car too loose on exit. the shocks you have don't have the adjustment range to dial down the exit rotation on their own so that probably won't work.
adding more front camber will increase front grip everywhere, but that means possibly too loose on entry and exit as well. basically, if you really want to free the car up mid-corner you are going to have to throw away your current entry and exit balance. once you've freed the car up mid-corner, then you can look into ways to tighten the entry and exit phases.
my suggestion based on the above would be to reduce both rear camber and spring at the same time. add in more front shock and a bit of rear toe in. the camber should free the car mid-corner, the toe, front shock and softer rear spring should stabilize it on entry and exit. it might not be the ultimate solution, but it's a shot.