Pray!
I've upgraded on this route as an Elite before so its not unheard of, call as soon as the 4 day window opens and hope you can get a confirmed U/G then, you don't want to wait until your at the gate

, I did once i'm sure I wore a chunk of the carpet out while I was waiting, luckly I was upgraded.
You probably stand a better chance out of YVR but I haven't flown this route for a while so i'm not sure what the loads are like now, but I had a 100% U/G record YVR-HKG when I was Elite.
Good luck^