I agree with DJMeatBall, it's doubtful NW will allow this but the only way to be for sure is to call and ask.

China's a "special" market to NW because of the heavy traffic to PEK/PVG... which is also why PEK/PVG see B744 service instead of B742 . I was rather surprised when I found out NW was going to 6 weekly flights (down from daily service) to NRT from PVG.