I'm looking to upgrade a one way domestic Business Saver award to First as no business seats are available for the flight I want to change to. The only issue is that the original business award was booked by a friend out of his account and I'd like to have the extra 7.5k come out of my account? Will this be possible or will they be looking to credit back the 25k and debit the entire 32.5k from one account?