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.
Track / Autocross setup: Forgestar F14 (21.8lbs & 23lbs)
Front: 275/35/18 Continental slick on 18x10, Rear: 305/35/18 RA-1 on 18x11
Drift Setup: Front: 275 Continental slicks, Rear: 255 Michelin PS2 street tire
Laguna Seca previous record - 1:49:498