I assume you have already seen the small image on the
JCW site (
http://www.johncooper.co.uk/JohnCoop...ort%5FBrakes/).
I don't think they have rear brake cooling vents in the mini-challenge, as I imagine it is the fronts that give out way earlier. The pic below shows the front brake air-diverters which take their air through the fog-light holes in the front bumper (I think). Probably wouldn't be too difficult to knock-up a DIY solution using some appropriately sized flex-hosing if you don't mind removing your lower-lights.