Ok, after getting some advice in the comments, and experimenting, this is the way I solved it:
- Apply a small measure of strength towards the depression
- If the current velocity is more than 30 degrees away from the center of the depression, slow the ball (apply strength in the opposite direction of the velocity)
- IF the ball gets very near the center of the depression, stop it and place it in the center
Thanks for all the tips. If anyone comes up with a better way, I'm still open to suggestions.