I pulled this from the "Crios mod" thread:
You can see the section of the muffler that the tip surrounds is oval in shape, so this round tip you have does not seem like it will work. It is a single hole, split down its center, but it's not round. I'm nor sure where you got it from, but that looks like something universal.
On the older cars what Porsche had for a tip modification was a chrome surround that would clamp over the original tip and stick out slightly from the rear.