Hey Monkey

,
(it sounds funny gotta admit)
Anyways you could buy a front of case 4 fan variable speed controller, or you could get the volcano 11, which is much lighter and efficient than the volcano 9 (which has a heavy copper insert). this HSF comes with a fan speed controller.
However, it seems as though you would like to build one or buy one seperately to use on your existing fan. that will be hard to find or build. <_<