WN is not an option for the OP because this is an international flight.

As others have said, there are no coupons, no tricks, no nothing to avoid bag fees.

In the future, before buying a ticket, be sure to consider bag fees in the total cost of the ticket, and shop accordingly.

Sadly, auxiliary fees are here to stay. Air travel is a commodity and people overall buy based on price. Because profits are razor thin, airlines need the bag fees in order to compete with the fare. Only way to undo this is for the US government to define what is included in the airline ticket, such as one free checked bag.