Well, I just try to help here... I assume most of you know already; there's a website that help you to book award flight on NW.
http://usr.v7.com/wpaa/
I played around the date and route a little bit and did find some open seats for the MSP-HNL and ORD-HNL routes. While it is true that NW doesn't release any seat on the direct flight from MSP or DTW, they have connecting flights out of LAX and SEA that have quite a few seats open routinely. Take a look!