Unfortunately I don’t believe that’s possible...I’ve only flown into YVR 3-4 times but you always seem to be directed right to customs with no possible “paths” back to the departing gates, presumably because it’s US preclearance?

Either way, I’ve found Canadian customs to be decently quick if coming from the US. The bigger slowdown is the US preclearance when you’ll head back for your LAX flight...THAT takes forever i.m.e.