Employee,
Just FYI (you probably know this anyway!) quite a number of credit cards seem to give lounge access.
E.g. I have a Citibank (HKG) Gold Visa card that gives unlimited access to all NW lounges Asia/N America - whether or not flying with NW. This is very country-specific however; last time at MSP they had to get the rule sheet out - I noticed they take the HKG card, but not the Taiwan card...
Anyway, just FYI. Also works with supplementary cards...
Angus