I did the same trip last year, J/Sed with CAL no problem going to HK, however on the return leg, flight was restricted due to cargo (from the CSR agent this happens often!) and there was a few non-rev trying to get on also. So I went to UAL's counter and flew HKG-SFO back to the states and found my way home then. I did brought a ZED fare for CX (HKG-JFK) also but figure I can get on the UAL flight to save some $$. The agent in HK was pleasant to deal with, they know exactly what Jumpseat was, taxes was minimal (if I remember correctly I think it was $15)
Have fun!