Did you see the NW promo for triple miles when connecting through Memphis? Just thought I would throw it in since you mentioned a routing through there. When I checked a routing online to see if I could take advantage of a unique trip to take advantage of the bonus, the only difference in the price was the PAX FAC charge. I know this doesn't answer your question and the post about calling the airline is as reliable as checking unique fares and getting six quotes on six different calls.

I also recall a trip to Australia a few years ago on Quantas that allowed us to add a stopover for an additional $150. We did New Zealand for a week, another couple did Fiji and the other three couples did Hawaii...well overdue for that trip again! Happy flying!!!