Yes, acceptable routings to Japan on UA and NW include routing through Hawaii (even on NW frequent flier tickets). MPM is Maximum Permitted Mileage, which is something like 20% over the great circle mileage, and is calculated segment by segment--obviously JFK LAX HNL NRT is more miles than JFKNRT, but if it falls w/in the MPM, you are allowed. Another example that might be possible would be a JFK-SEL-NRT routing (on KE or OZ)--again you overfly NRT, but you have the MPM to get in the flights (probably could even squeeze in a stop in someplace like Pusan, to take it to the extreme).