The hardwiring of the Windows 8 Keys as the default keys instead of the more often used Function Keys drove me nuts. I have far more use for the F1 to F12 keys than the Windows 8 Keys, particularly in Mac OS X.
This is a hardwired feature of the Microsoft Sculpt Mobile Keyboard.
The only solution which works is to sacrifice the Windows 8 keys by permanently setting the Fn in the down position.
I did this by popping off the Fn Key and taping the switch in the down position. I used double-stick permanent mounting tape for adhesion which was then covered by black gaffers tape.
I love that my Function Keys now work as I want them to.
Sure, I no longer have keyboard support for volume - compared to the Microsoft Bluetooth Mobile Keyboard 6000. But I do gain a hardwired Home and End Keys. And I can easily create a macro to control the volume.
Since the Sculpt Keyboard is also half the price of the Keyboard 6000, this hardware modification saves me $20 every time I wear out the keyboard.
I wouldn't worry about battery life from keeping the Fn key pressed down since usually I turn off the keyboard when not used - when the keyboard is used as a mobile keyboard. When used as a desktop keyboard, we will have to see if battery life is reduced.