Looking to book a one-way ticket (CEB-JFK) for next year. I have no points on EK. When I look at paid-fare options, I see I can get a FLEX fare for about 1050USD, with an option to upgrade to business for 91,260 miles. Can this upgrade be confirmed at time of booking? My thinking is that I can transfer Membership Rewards points from my AMEX account to cover the 91,260 miles for the upgrade.