Starting with Windows 2000, Windows has built-in support for remapping keys:
...yet this seems impossible to do because this so-called function key does not send an ID-number...
If it didn't it would be a dead key. I'm sure the hardware generates some sort of event but the keyboard driver might chose not to propagate it. In that case you'll probably be forced to write your own filtering/remapping keyboard driver and install it on top of the existing one.
I have no experience working with these thing but perhaps someone else on this board does?