Movement based on collision on a custom mesh

I'm working on a 3D racing game, with a custom mesh (a semi-cylindrical downward spiral) as the track and a sphere as the player.

I've attached the mesh collider component to the track and a rigid body component with a spherical collider to the sphere (with gravity and kinematic off). When I place the sphere at the beginning of the track, it happily rolls down the track till the end. Great!

Now, I want the player to be able to move this sphere left and right (to escape obstacles). To accomplish this, I'd need to be able to define fixed local axes for the sphere (so Z represents forward, and X represents right). Now, the physics based rolling of the sphere rotates all the axes, so I can't use transform.forward and transform.right (since they're always changing).

How can I go about accomplishing this? I was thinking of may be using the collision normal (of the contact point of the sphere with the mesh), but I'd like to know if I'm missing something.

Thanks.