I love to use the billiards method of practicing for lag putting. It has to do with lagging for the break in pool. Using the same method I have students stand on one side of the green and try to get the ball as close to the opposite fringe as possible without hitting the putt hard enough to reach the fringe. By taking the hole out of the equation the player is freed up to concentrate on just distance control. This can be done at different distances to help with pace control.
Important to have the student do this on the flattest part of the green. If flat isn’t really an option then uphill is the next option. Very important to not let the player use a hole in this process.