Andi,
There are some tools in the Win95key package that give the key codes if they are reported. You could try them and if they do give a key code you may be able to do something with the information.
Win95key (from hobbes) works with PS/2 keyboards only (usb keyboards don't work) but does allow the use of all the keys on 'multimedia' keyboards so there is a possibility it or the tools could work for you.