I practiced inverted stall turns a bunch.  Inverted pass, push to vertical, correct with rudder if the line gets off, stall turn, push to recover inverted, etc.   This isn't too risky so its a good one to practice with a real airplane.  Correcting the upline with the rudder was really good practice.  I also used to  do inverted figure 8s and use rudder in the turns.  Less difficult than the inverted harrier mentioned above, which is also great practice.  
Then I practiced torque rolls on the sim a bunch.  Finally got to where I could correct without thinking.   I still practice TR's, on the sim or at the field, all the time.  I find this orientation is one I have to keep up on. </p>