I discovered that the in-dash cup holder in my Subaru Outback (1998) has a quick release lever at the back and a fairly flat face, so I made it into my iPad mount. I've attached 3 photos of the installation.
I cut a piece of 1/8" plywood about 6"x7" (vertical) and marked it for drilling against the face of the cup holder. I drilled two small holes right through the plywood and the front of the cup holder. I cut out an oval in the plywood so that the cup holder release button could function and hold the cup holder against the dash. Then I glued two 2"x6" strips of plywood at the top and bottom so that there would be room for the screw heads to stick out without touching the back of the iPad.
I attached two 2"x6" strips of heavy duty velcro to the plywood strips and in matching positions on the back of my iPad, avoiding the apple logo which is the wireless antenna.
I screwed the plywood onto the face of the cup holder with two 3/4" screws, and that was it, ready to slide into the dash. The only drawback is that the heater controls aren't easily reached any more - but hey, it's summer!