Well I guess later is better than never!
Ive got my inspection this month and have been able to get mt '15 335i into an emissions ready state while running Stage 2 w/o cat using an angled spacer.
Its easily accessible from the top side of the engine bay and takes about 5 minutes to install. *For offroad use only
From my testing you'll need to keep out of Sport+ mode because it will throw a code during spirited driving. Prior to the angled spacer I would not get a ready state from the Cat check and an efficiency code. As you can see in the attached images Cat check passed.