One of these ways is the next method, the ghost ball. By the way, make the spot something that doesn't move. If you aim at that girl's nose, you will miss when she moves. Imagine a ghost ball off the table, about the same distance outside the rail that the target ball is inside the rail. You can deal with them in the same way that you do with the other methods.
Some adjustment has to be made, depending on how far the object ball is from the rail.
Experiment, and let me know if you hit upon a good method. You can actually measure the position of the ghost ball, with your cue or fingers. And it should work about as well, in most situations. Guess where the point Y is going to be. Then find point Z on the rail, and find a new Y midway between Z and X. Repeat if you were not very close the first time.