you mean like make 2400RPM fan go faster?
Cuz, in theory you could do that if you attach the ground wire to the -5v or -12v rail, but dont know if the fan can handle it.
If the fan is adjustable (like TT Smartfan2) they have a little pot that speeds up/slows down the fan or can be controled by a temp sensor.
So I guess it all depends. :shrug: