i did this mod also. and it works.

bit i suggest that u connect the fan not directly to the psu, but to a male molex, then u plug it to the female molex from the PSU.

and for the variable fan controller, just add a variable resistor. if you want you can also add transistor and capacitors, but that one i really dunno how to design the circuit. dun ask me

for smart fan, i dunno how to do it... lolz (erm.... if u leave the fan as it is and dun mod it, the mobo can control the fan speed aka smart fan)