I think most people who want to fan mod slims just cut the blue wire. You can also pull it out of the connector if you lift the little white clip with a knife as you pull out the female pin.
I've been making fan booster mod chips for the PS3 fans that increase the PWM control signal about 20%. I just recently tried one on a 360 slim fan and it doesn't work, the fan control signal is different. The fan pulls the signal high when disconnected, that's why cutting the blue wire works. I'm going to see if I can make a chip that properly controls the 360 S fan.