When I was a kid they strapped a couple of wooden blocks to the pedals when I got my first 'Big Boy Bike' :-)
Actually, you could rig something that would work, but I am assuming you want something readily convertible between different drivers. Of course, it would have to be secure. Losing her reach to the brake pedal when she needs it could be unfortunate..
'08 E-150, std roof, wb, 2wd - basic cleanup done. Working on rough layout of 'furniture'.
Pretty much everyone will step on their 'willy' once in a while.
I usually make it a point to stop and put on my golf shoes first..