the guy you mention Steven is the guy that does them indeed - he homologates rally cars

but as many people above think its just a case of beat them into a bubble shape - the wings are actually flared quite a bit wider aswell, and this has to stretch the rest of the wing to do so, so all the mounting points have to be cut off and re-welded on at different angles on spacer mounts, and new fixings to allow the wings to pull into shape.

then the front of the wings become extremely tight to get the headlights and the small side light sections to fit correctly.

although its very easy to change the wings, it will take a day or so of mild fettling to get everything to fit snug and happily again.