The last post shows that it is possible! And he even stripped the back!
Honestly I don't think you will ever want to remove and reinstall a cage. You could go the route of an add-in roll bar. I know they make one for the E90 and E92 (E93 no idea) so you can run racing seats and a harness without a cage. They also are somewhat removable if you only do a few events per year.