AirBerlin will also go to Dusseldorf, so when you look at your dates, take a peek at that routing, too.

The other oft-mentioned routing from the USA on Avios is the Air Lingus Boston to Dublin route. So get from San Diego to Boston, Boston to Dublin, then to Oslo.

Don't forget to check Ryan Air once you've routed to Europe, might be the easiest and most affordable way for short hops.

As an aside- I'm taking the Amtrak coaster from OSD up to LA next week for a flight. That worked out pretty well.