Dutchie,
Out of interest, facing the same problem of getting the youngster into a car seat in the back and then worrying about quick access to the back in the event of an accident, i went the route of contacting the NHTSA (national highway traffic safety administration) for approval to install an airbag disconnect switch.
Once i had approval i ordered an airbag disconnect switch ($199)which is key operated with status indicator lights on and must be installed in the drivers line of sight. Installation was easy just had to crimp new connectors onto the two wires running to the airbag then plug in the disconnect.
My kid now rides up front secured in his child seat safely and legally and its soooo much easier to get him in and out.
Seat extenders are still a great idea for general rear seat access though.
Pete