Currently CASS is domestic only so that eliminates all cargo airlines for you. It also eliminates the "real" jumpseat - you'll have to ride in the back on all pax airlines (US carriers). I looked up NWA and they are flying from Detroit to Osaka, Minneapolis to Nagoya (through Narita), and from Minneapolis to Narita (pretty long drive from Osaka I think). I’d say, try to contact NWA jumpseat coordinator and maybe he/she can give you some feedback?

Also, is the left seat worth lots of extra dough? If so, if you really have to, the coach ticket from Detroit to Osaka and two weeks later back to Detroit will cost you $1009.20 ($1056.71 Total Price) according to their website. I'm just saying it might be an option if everything else fails. Good luck.