If I understand you correctly what I did was made a small block and placed it just on the tip of the rim and made it invisible. And set it so when the ball collides with it (Solid, Immovable) it will bounce off. So in other words the ball has to go over it to hit the rim and go in to score a point.
Play it and see what I mean - Left/right arrows to move and up arrow to jump...
This will show you better than I can explain it.