Basically the 172 wings are 1.5" wider than the dynamiques.
Check out "Combine04" clio (use the search button) and you can see he has cut the bumper to fit and then used some sealant.
The problem with using RS wings, is not only the cost, but you need spacers too, or the wheels look a bit silly.
IMO it is an excellent mod if you have the money lying around. Don't listen to people who say its pointless and a waste of money, as providing you buy 2nd hand you will get your money back.
Expect to pay no more than £300 for the wings, replica skirts and bumper.
Sam