The LCY-NYC is a mainline service and therefore will not be operated by a subsidery such as Cityflyer.
Now a "w" pattern does seem the most likely. Simply because they do not get paid the same B2B payments the LHR crew get and the airline get three more working days from the week out of their crew without having to give extra days off! The LHR crew have been doing the LHR-EWR/JFK-MAN-JFK/EWR-LHR "W" pattern now for well over a year without the B2B payment.