A couple of things will come into play here. If your car didn't have the hatch shade from the factory you don't have the metal brackets that the mounts screw into. So, you can go a couple of routes. You can pull the rear trim panels and look at the back side, there's an indentation that clearly shows where to cut the holes for the mounting pads. You could cut them out and hold the mounts in the holes while you put the shade in place. It'll look stock and the shade's spring tension will hold them in place. But if you need to remove the shade for any reason the pads fall out and its a minor PITA to put the shade back in place. Another option would be to not cut the holes, just screw the mounting pads to the plastic. I've seen this done and it works, but since the pads are meant to be countersunk it'll look tacky. Or you can fabricate the metal brackets and bolt the pads to the car and have a setup as good as factory. The last obvious answer would just be to sell the shade for a nice profit on ebay and get the hatch tinted.
BTW you'll also need the hatch trim panel with the steel reinforcement for the shade, otherwise it just won't work.
The normal panels can be cut but the steel reinforcement bar has been discontinued from GM. | 
