Could you give more precisions ?
Rigidbodies do not provide collision on their own (or I missed something), the gameObject must also have a collider attach to him (e.g. BoxCollider) to collide with your CharacterController
I’m not entirely sure, but I don’t think you can.
I’m pretty sure they made it this way on purpose. Sorry.
Kudos,
SilentWaffle
look at this previous post