Interesting thread! To me, it seems like what needs to be sharpened is a little more than hand-eye coordination - it's the brain function that goes along with the 'reversed' inputs needed depending on the plane's attitude.

For example, I was told to watch the inboard wing tip and 'push it' with the rudder stick for inverted rudder corrections. Sounds easy enough, but every time (I'm still relatively new at this kind of stuff) it feels like a big, rusted gear starts to turn in my head and the input is too delayed to fool the judges.

Another example could be prop hanging - when the canopy is toward you, you steer the nose. When the belly is toward you, you steer the tail. Same rusty feeling in the head.

I can't think of an exercise to help improve this hand-mind-eye relationship other than flying and using the sim, but it would be really cool to find one.