Actually you don't need a full-fare ticket to get on the NW upgrade list, just your KL Plat number. This year I have been upgraded 5 to 6 days out as a KL Plat on domestic NW flights.

Continental upgraded me twice at the gate but it's uneven (prior to SkyTeam). It is truly a NW-KL relationship for sure as far as upgrades but my main point is you should get upgraded on NW flights in advance if you are KL Plat provided your number is in the record.