Sounds more like you have to tap into the senor on the motherboard for this. The only mods i've seen that are kinda like this are on computers but not for fan control but as a EQ display for winamp. Theres fan controllers out there for PCs that let you control the speed of the fans and tells you how many RPMs and such. They can work on a Apple aswell since its not software based. Just plug the controller into where the fan connects to on the motherboard/logicboard and connect the fan/s to the controller.
To live is to let die