Can't be done... I went through this hassle last year and actually had to go back to stock exhaust to pass. Now a days the emissions places have to scan the vin# into their computer and then connect to the ecu. The ecu also contains the vin so it makes it almost impossible to pass.

Hope you figure something out though and I am sure a TT 350 is a blast to drive.

Oh one other way is to move to a county that does not have state required emission testing