there was a post a while back with a hitch hider, so if you have a hitch on your car, you would put the key in the hitch thing and take the metal key with you, might be an option if you DON'T have keyless Go (I can't think of what BMW calls it)

__________________
2006 BMW X5 4.8is Lemans Blue/Beige/Dark Maple
-Nav, Comfort Seats, Heated Steering Wheel,
Rear Airbags, AUX Input
2009 BMW M3 Space Grey/Black/Carbon
-all options