[piers.singer]

Depending on your car (and your skill), you may or may not be able to incoporate upper and lower grille blocks without substantially altering the look of your car. Judging by your garage entries, I'd say that the Avensis and BMW don't have recessed grilles and so you could make a simple mod that way, if you created grille blocks of a similar colour to how they should appear otherwise. On the Clio this could be trickier as the upper grille is essentially a large panel gap between the bonnet and the bumper. Still, if you filled the space with some dark material, it could still be adequately inconspicuous on the move.

What I have also seen done is grille blocks being placed behind the original grille. This is a bit of a compromise from an aero perspective, but it should still raise engine bay temperatures for better efficiency and is practically un-noticeable.