FM signals are line-of-sight only, although they reflect off most surfaces. Your best bet is to get a highly directional antenna like a Yagi (one designed for the FM band, not a TV antenna) and point it right at Mt Hood or Mt Adams, if you can see either one of them from your house. The elements on the Yagi should probably be vertical, but you can try it both ways. The signal strength meter on your tuner can be used to fine-adjust the antenna direction. The bounce signal will be strong enough to pull in IF you have a good enough antenna. Otherwise, there's not much hope.