I think the whole point is to put the key where it's accessible when you get locked out. Kinda hard to get to the floormat if you're not inside the car

I still think the best solution is to put a spare key in her purse. Only problem is if she locks her purse in the trunk, then you'll have to make another trip out to unlock the doors lol.

 

In case anyone cares how this turned out.......

I took a cheaper variation of Habious' idea. Rather than get a uncut key with remote and program the remote to unlock the car, I got a cut key without electronics from http://www.toy-lex.com/index.html for $25 bucks. I attached this key behind the license plate, like Lexucan recommended.

With this key, a thief could open the door and run down the battery. The engine won't start because it has no electronics.

But after opening the door, my wife can open the trunk. The real spare key is hidden in the trunk, jammed behind the inside trunk release. No one would ever find it there.

If anyone has better suggestions, I'm all ears.