Hi Jatin,
There is no any separate control key as such for REM subcontracting even I have doubt that operation sub-contracting is possible in REM scenario. I have never worked on such but in my understanding if you are
using a reporting point backflush then this may be achieved.
You can use direct sub-contracting where this is possible means keep subcontracted incoming SF material as procurement type F and take the help of MM expert to show the raw material if any in the PR created. In this type of scenario PR is created for subcontracting material and you can track it like a separate subcontracting material.
Also for more info refer below threads,
Operational level subcontracting in repetitive manufacturing
Repetitive manufacturing:subcontracting
Regards,
Narresh