To control the pan, you will need to add an angular force. To do this, you use phent_addcentralforce with a veclocal off center. This will apply an off center force and effectively rotate (ie change the pan) of your ball.

Regarding your requirements that the ball not roll unless it's on a hill (Guessing something like Marble Madness perhaps? ), then as long as gravity is set within the Physics Engine, this is exactly what will happen.