Mapping Key (e.g. F15) to Fn Key with no Fn Key on keyboard None of the keys in my keyboard (Microsoft Sculpt Ergonomic Keyboard) are natively recognized as the Fn key by OS X (I checked with Mouseposé)

I have Karabiner and Keyboard Maestro installed but: 


Karabiner doesn't seem to have a template to map things to Fn
As shown below, there doesn't seem to be an option in Keyboard Maestro to enter by hand Fn


How can I bind a key (specifically I am hoping to map F15) of my keyboard (e.g. F15 to Fn)?
Try the DoubleCommand (free, sourceforge) project. According to the features page, you can map the fn key, though it's only listed as partial support.  I don't have any personal experience to share...