Practice the same as the first two shots, while swinging your arm to 9 o'clock.
Finish off swinging the arm to 10 o'clock and you will now have four specific distances that you can consistently pitch the ball. Distances will vary from player to player as in full shots, but once you have them established you have a tried-and-true method on which to rely.
After working with the 7-8-9 drill, you'll find yourself 40 yards from the flag on the course and can say to yourself, "OK, this is my X o'clock shot." And now you know for sure that if you swing your arm to that position, the ball is going to go about 40 yards.