I built an internal and manual fan controller for up to 5 standard 12V PC-Fans. It should fit many different printers, but I designed it for my Replicator-Clone.

The Fan controller I used was the Aerocool F5XT:
http://www.aerocool.com.tw/en/fan-controller/single-bay/f5xt

The circuit board can be loosened very easy and the buttons / sliders are only clipped in place.

First I printed the "Mount Pattern" and drilled the mounting holes and the slots for the sliders (using a 3mm drill).
Then I printed the spacers, buttons and covers and all fits together with only 2 M3 Screws (or other if you use a bigger drill).
Note: The cover does not have any holes, you have to glue it in place or (like me) drill the holes by hand. I did this, becaus a miss-aligned the mount pattern a little bit and could fix it in this way.

I added the Slider Button V2 (tighter tolerances). I also Uploaded the .stp for the slider button so you can adjust the design, if you find they wont fit properly.