The upper bumper aero grille can be installed on a stock S bumper with modifications, mostly on the grille itself. It’s basically a one shot deal, and those grilles are hard to come by (it’s the small one below the hood). I plan on doing this mod and just making sure I don’t miss a more updated or easier procedure. These are the two links I have, the first seems to be better because of the update at the end.

http://www.motoringfile.com/howto/MI...ll_install.pdf

https://www.specr53.com/blog/diy/mini-aero-grille-diy/