Batman, you could - but everytime you wan't to turn on your LEDs (
) you will also be running your de-fogger. Not sure that's the best option!
Why don't you just source a direct connection from the fusebox as Nimbus mentioned.
Search or post an appropriate thread, therea number of guys on here that are very good in that area i.e. Nimbus, Partialwave to name but two. All very clever and resourceful guys.