Even though I already had my boarding pass, I stopped by the business class check-in before my flight and asked again. This time, they informed me that there was one seat remaining. I happily paid $300 in addition to 25,000 Advantage miles and they issued me a new boarding pass along with a day pass to the Tokyo Narita Admirals club. This lounge is nicer than I ever imagined it would be. Plush leather chairs, the highest speed internet I've experienced in a month, all you can eat sushi, snacks, coffee, beer, liquor, magazines, tv, and other things I'm probably not even taking advantage of.
Budget travel is an adventure, and I'm not going to turn into a complete diva, but this is a VERY nice way of capping off a wonderful trip around the world. See you tomorrow in Dallas-Fort Worth (although, it's already tomorrow here).