Object ball frozen to cushion

In this shot, the object ball is frozen to the rail and you have a very steep angle with the cue ball.

The secret to making these kinds of cut shots is to actually aim to miss, just a little, and play the cue ball into the rail first with low english in the direction of the object ball. The cue ball will rebound off the cushion and into the object ball to make it into the corner pocket. This is actually much easier to execute than to try to cut the ball in.

Try it as shown. As you get more proficient, move the object ball further down the rail until you reach a point of difficulty or low proficiency that would not benefit you in a game. Practice this shot and know you percentage for making it one diamond out from the pocket, 1.5 diamonds out, 2 diamonds out, etc. That way, when it comes up in a game, you will know whether or not you should shoot it, or play a safe instead.