So these are the issues that I ran into when mocking up the lip:
First, you can see that the lip isn't really straight to begin (especially on the driver's side of the bumper). Also, it doesn't quite line up with the bottom of the bumper:
But when you do adjust the lip to sit flush with the bumper there isn't enough material to reach each end of the bumper's corners:
And don't even get me started on where you would have to drill holes into the lip to match the holes in the bumper for mounting!
Overall, I took a gamble and knew that aftermarket anything would most likely give you trouble when fitting them to the car... But that I really wanted to see this one through..