Honestly, for the seat guarantee, I would use Marco Polo Club because it is a Club benefit. I believe that the MPO Club call center is open 24/7 and can do it for you whenever you call. I expect you can choose which fare you want, either YBHKMLV, and waitlist it if it is sold out and then call MPC to change the waitlist to confirmed and then have reservations or your TA ticket it, depending on with whom you made the waitlist reservation in the firt place.