Remap caps lock key to toggle FN key?

I'm looking for a way to remap the FN key to the Caps Lock key on my i7 MacBook Pro.

I almost never use caps lock, but I often toggle the F keys between the F1-F12 and Apple's functions - volume, keyboard brightness, etc, and that means going to the keyboard prefs in system prefs, which is time consuming and annoying.

I've tried an app called PCKeyboardHack, which reassigns the keycode sent when the caps lock key is pressed, but the fn key doesn't seem to have a keycode, I'm guessing because it changes the keycode of the f keys. I used an app called Full Key Codes 1.2 to try and find it, but nothing shows up when just the fn key is pressed.

FYI, I'm using a few different audio editors, such as Protools, which use the F1-F12 keys.

Any ideas?

Thanks!