Originally Posted by ComputerMike
What you want is called a fan bus. Its used by computer geeks to manually control different and multiple fans within the computer case.
or google: computer fan bus
What about just using a ball valve or a gate valve to adjust the amount of air flow, either in front or behind the fan, that is what the guru does. The fan is not a variable speed unit and is only adjusted by the flap after the fan, thus altering the air flow. Of course the hard part would be fabricating some kind of box to mount all this.