For business flex, you should be able to make flight bookings (reservations, including seat reservations) without actually ticketing the flight. Payment only occurs upon ticketing. Ticketing can be done as late as a few hours before the flight (although in that case e-ticketing may no longer be possible, so you'll want to ticket the flight a couple of days before flying). The only downside to this is that you can't upgrade until the ticket has been issued.