I saw this here - 
http://www.reichhard-motorsport.com/ 
 
INOX-Kat.-Ersatzrohr für Vorkat. aus Edelstahl für Clio3 2,0l 16V RS.
H27155CL3 
 
Preis inkl. gesetzlicher MwSt. zzgl. Versandkosten: 
280,00EUR 
 
You have to take your exhaust manifold with the pre-cat off and send it to them. Then they cut the pre-cat off and weld hmmm dunno the english word for this but hope you understand - they weld a flange on both ends 
something like this so you know what I mean and after that you can put either the decat pipe on or your pre-cat back on :tongue_smilie:
 
Hope I helped 
