Take the MAX to Hillsboro, then follow these directions. http://www.bikely.com/maps/bike-path...Nestucca-River

That ride is breathtakingly beautiful and as secluded as they come in N. America. From there, camp at either Cape Lookout State Park (amazing park with post-card idealic camping right on the ocean *BUT* there is about a 1000ft climb in and out, assuming you head South after camping there.) or stealth camp right where the 101 turns South after Beaver

It would ad a day or maybe two and some climbing, but is well worth it.