If space is available in World Business Class on the day of departure, chances are no one is going to walk up and purchase a full WBC ticket.

Call NW, ask [politely] if they could contact Revenue Management Support to see about opening up a C class seat, and then use your miles.

Believe me, NW would much rather have a customer burn 40 or 50 thousand miles to upgrade than do an "involuntary" or "complimentary" upgrade.

Don't expect to do this at your gate, however. Gate agents have enough to do without a customer asking them to call the WorldPerks department, wait for the fare to be stored, and reissue a ticket! Try to take care of these things the night before or the morning of departure and you just may be surprised.

Oh! Don't forget, there may be a $50 Expedite Fee to pay at the airport!