it can definitely be done - but it wouldn't be able to stay circular. It would have to be oval, in quite a pronounced way, to allow the head to remain untouched. To make it truly circular, you'd be looking at changing the angle of the part of the ring holding the sapphires (along with the rest of the ring as well), which would almost certainly start popping out the sapphires.
I'd be a bit iffy about anyone who told you it could be done and still be symmetrically circular. And ovaline would squish parts of your finger.