From COC:
(1) General. Carrier, in its sole discretion,
will accept personal property of the Passenger as
Baggage subject to the following conditions:
(i)
Carrier will only accept Baggage for transportation on a flight on which the
Passenger is transported
You probably can get away with this but it clearly circumvents the COC terms at least implicitly. If you get caught, it will likely be considered fraud in that the passenger circumvents the $75 extra bag fee on two bags. Furthermore, if there is a lost luggage situation, then only the person checking the bag may file a claim. This is very likely where you will get caught.
When WN catches you, and they will if you do it enough, they would be within their rights to close BOTH RR accounts, and ban both of you from future travel.
Just my guess.