You could probably get away with using this method to get into the WC (WorldClub). But I doubt that you'd get into WBC (World Business Class) with a Y ticket....

And it seems to me that you'd spend an awful lot of time booking the ticket and checking in, then getting yourself "unchecked" and refunded just to get a free beer or two and a nicer chair to sit in.

Also, you run the slight risk that NW might notice you have two tickets booked for the same time and cancel you on one (or both) of them. I'm not sure if they have the software in place to do that or not (I think CO does).