I have never seen a rt ticket that was cheaper than a oneway on the same airline (so the throwaway strategy generally doesn't help).

Regarding the KA holidays, if you can pull one off, I would definitely go that route, especially if you can talk them into letting you open jaw. Even if they say, "no" (likely), you should take comfort in the fact that there are only around 6 flights per day between PEK and PVG and most run pretty much on time because they are tags to high(er) priority international flights.