Do you mean with just collisions, or keeping points attached on a ring but free to slide along it?
With collisions, I think once both sides expand beyond some amount the ball will be held in place by the ring, (like a belt on someone who ate too much christmas dinner!)
but before that point is reached and the ball is only slightly larger than the inside of the ring, any asymmetrical forces can cause it to pop out on one side. To stop it sliding out but without actually attaching it using OnCurve or Anchors, you could use the friction goal I posted here.