As I work with these Mirage panels it seems pretty obvious that the intent of the original designer was to bond them on. There is even a bonding strip on the back of them at the top edge. I located the panel where I wanted it with screws in the fenderwell and spoiler holes, then scribed a line along the top so I could see its location once I removed it. Then I ground about a 3/8" wide strip all along the top and front edge.
Using a two part epoxy product by SEMS called "Multi purpose panel adhesive" I filled this area and pressed the panel into place. This stuff is ridiculously tough, you cannot even pick it off with a screwdriver. It seems to have a tenacious grip on the plastic. Some creative clamping was required to hold it all down tightly.
One thing I learned about the mirage panels is that they have quite a bit of memory. Apply some heat with a heat gun to a warped area and they will pretty much straighten themselves back to their origonal shape. Or if you really heat them up you can convince them to stay somewhere else. In this pick below the panel was sticking 1/2" or so away from the fender lip. I heated it up at the bend and clamped it into place util it cooled. Now they are nice and tight together.
As further proof of my theory that these were origonally designed to be bonded on, look at the lineup of the factory quarter panel and spoiler installation. Then compare it to the one below it where I have the two bonded on. Look Ma, no Rivits!