I've done it many times, although you can't book open jaws on the Web. Just finished a nightmarish booking of EWR-NRT-SHA; NRT-GUM-HNL (stop-over); HNL-EWR. Several CO screw-ups along the way convinced them to make nice and wave a black-out date and snag standard BF seats for me out of inventory. Best use of 120K miles I could think of.