You can't have it all ways:
1. If the RFM prohibits it - don't do it - endex.
If the RFM (Bronx this is for you in mono syllables, just in case) such as the B3e doesn't mention it, it is because section 2.1 covers it: One flight crew in the RH seat. IF a helicopter is burning and turning (at idle or otherwise) then it is deemd to be in a state of 'flight' because YOU ARE LOGGING THIS FLIGHT TIME - Bronx. Don't try to tell me otherwise. No-one will tell me they stop logging flight time everytime they go to idle or sit on the deck for minutes on end doing nothing and then start logging time once they wind the throttle(s) up and or go flying again. So the cab is deemed to be in flight mode during this hiatus in the actual flight - Thus a pilot MUST / SHALL be present and in the R H seat. Endex. Capiche?
So the pilot who exited his 350B3e for a fluid check exited against the RFM rules. QED.
Cotteral - you are in the wrong section, you need - wannabees.
SuperF - no need to ban anything - it is already prohibited from leaving a cab which is running.
LASJayhawk - if your ops 'demands' that you cannot shut down everytime - then negotiate with the OEM's to change the RFM. It's not easy but if a major player in the fraternity feels the need to do this - it will happen and you will get an exemption.