I've been thinking about writing a quick tutorial on this.
I've got a Xilence Redwing 120mm which I have already pre-drilled waiting for such a time where I can be bothered to actually get on and mount some LEDs in it. I had planned to make it today but had to work on my car instead and that took all day.
For this one I am going to mount 4 per side, for a total of 16 LEDs. Orange again (Thanks for the Orange bug goes to G-Dubs)
I will be running 4 LEDs in series 4 times around the circumference of the fan.
If you can be patient I will get this done over the next couple of days and will also put some of the theory in the tutorial so you can adapt for your own needs.