yeah it is possible. just disconnect your rear speakers and put them into your 6x9's. there was a parcel shelf on ebay for sale with 6x9's already in but not sure if its still on or not.
if the spare key was in the car and you tried to lock/unlock the car by pressing the button on the handle it would alert you by making a noise. you maybe could have went back in the house and placed your key down??