Book all the potential options and later cancel the unwanted routings. Eat the $12.50 partner booking fee unless you booked on the Summit card.

Any modifications result in reissuing the ticket. If there’s still award seats available, you *should* be able to do it by just paying the difference in points & fees. However, some have reported losing J/F space in the process, so be careful if you go that route, even in Y.