He challenged me to see if I could turn a basic Matchbox unit into an AppMate-compatible iPad accessory. I created an aluminum band around a Matchbox car's belly, attached two "pads" (folded Kleenex wrapped in aluminum foil), and ran the app in "Paper" car mode -- which requires only two points of contact on the screen at any time.
The video that follows demonstrates my success.
So what about the other features? Car identification and headlights and so forth? They're possible, I found out, by using additional touch points that follow the layout on the retail units (see the picture at the top of the post) but required far more calibration. I managed to get the headlights on and Lightning McQueen "recognized", but my homebrew touchpoints weren't stable enough for normal game play. It could be done with a little more crafting, however.
Like the actual Disney-branded version, my homemade car requires a touch on each side of the vehicle, to connect with my aluminum band, allowing my two capacitive pads to register as individual touch points.