Tuning a stock 99 WS6

My T/A is bone stock except for the K&N airfilter I installed. Without doing any mods at all (no bolt-ons, exhaust, headers, etc) what would you guys recommend for tuning? For the time being, I want to keep this car as stock as possible, but I'd like to squeeze out a little bit extra HP and maybe some fuel economy.

MAYBE if the car is an automatic... otherwise get some mods,and a K&N filter does not count as a mod :)

Haha...it's a 6-speed car. I'm debating getting true dual exhaust, long-tube headers, airbox, etc. However, I also kind of want to keep it stock, you know?