BKK-NRT on NWA or UAL is pretty easy to do with the gate agents. They are very familar with the process once you mention that you are a pilot. Expect to meet the crew before they transit security, in front of the check in counter, for credential verification, and then seat assignment if available.
Your best back up is a ZED on Thai Airways. Thai Airways is also well versed with non rev's and it's seemless traveling on them when seats are available. Moreover, they fly between 4-5 flights a day to NRT.
Enjoy.