Long story short, I am doing a bit of a milk run that involves YWG-YVR (overnight)-SFO-OGG.

I have no status so I'm paying for the bags out of YWG to YVR. My concern is that when I return to YVR in the morning for the next segment on UA to SFO, they will try to ding me a second for the 2 suitcases we'll be checking. (I'm having flashbacks to a US-to-UA debacle at DEN last fall involving a similar set of circumstances.)

Apart from changing my schedule, is there any way to ensure that I only pay for checked baggage once?