You can try the Springwater Corridor path all the way to Oaks Park, over the Sellwood Bridge and then up through the cemetery. Then over to Barbur Blvd then take Barbur/99 all the way to Hall Blvd, hang a right and on to Washington Square.

The climb up through the cemetery is pretty stiff though, you'll either have fun or track me down and beat me senseless for suggesting it ;-)