Possible to get boarding pass from unrelated airport?

I have an upcoming trip KHH-HKG-PVG (CX) connecting to a separate ticket for UA PVG-LAX-EWR

I have a 4hr layover at PVG, with no checked baggage. It is possible to check in and pick up my boarding pass for UA in HKG instead of PVG so I can just do an int'l transfer at PVG?

I've never had luck with any airports in Asia accepting mobile/paper boarding passes...:o