I would realy like to know as well if an Audi blank would work. I always worry about loosing my key when away from home and would like to hide a spare in the car.
I also toyed withthe idea of switching the Lamborghini FOB key with a smaller physical Audi key and just having the lamborghini key hidden under the dash (assuming the FOB signal is required to run the car). This would get around a problem I have of my long legs hitting the Lambo key that sticks out 3 inches when driving.
Please go ahead an let us know if your theory works.