As in small spoilers that attaches to the side of the front bumper to add down force?
Usually found on track cars...
I remember seeing a picture of it on a mini, but can't find it.

 

I think I remember the MINI you're talking about - looked like a track car with a nice splitter on it as I recall. . .

Not sure about adding downforce, though - I think their main objective is to help smooth airflow around the bumper/fender area and possibly help divert airflow over the wheel opening, a notorious source of drag.

But I could be wrong. . .