If you have status with CO (Silver, Gold, Plat), you can have PDX put you on the bump list. If you don't have status, then the PDX agent will tell you to wait until you are at EWR.

I took a trip over the 4th of July to YHZ (LAX-CLE-EWR-YHZ) and they told me that they couldn't put my name on the volunteer list at LAX because I had no status on CO. I learn new things every day. Not like that on UA & US.