Go UA to FRA in upgraded C, then LH in coach to CPH (short flight). You should be able to book at United.com... use the multi city option and for the first segment do PDX-FRA, then the next segment FRA-CPH.. and 2 more segments in reverse to get you back home. Make sure you choose the upgrade type systemwide region 2 so that it will give you the correct upgradeable V/W fare, and check the box for "include Star Alliance flights".