Two options:

Call AA directly to book this. The AA RTW desk is amazing and can book the exact flights you need. There are plenty of threads here that talk about buying and ticketing in Japan. But basically you can Skype call 1-800-247-3247. Tell them you will purchase in Tokyo and have them put the ticket together with your exact flights. Make sure you ask them to price it in Yen. It takes about a day to be priced. Once priced, call AA in Tokyo (+81-3-4333-7675) and pay for it thru the ticket office.

Two, book the flights via the OW website and pick any ORD-DFW flight (either next day or earlier in the day that isn't as convenient). Once the website tickets it, call the AA RTW desk and have them change the flight to the one you want. Changes are free.