We have a standalone SFO-ICN flight. I don't see why you couldn't just jumpseat on that, unless it's because loads look better SFO-ICN-PVG. I'm not sure if this is still the case, but PVG was at times a "cargo only IN, cargo + pax OUT" destination, as China had prohibited entry from the US. IIRC, the ICN-PVG tag was to have our crews layover in ICN. Good luck!