Tricking the Emissions with on and OBD II motor

I have a question that so far no one seems to be able to awnser. So here is the deal nowadays when you go to the emissions station, and if you have a 1996+ vehical all they do is plug into the OBD II port and read the engine for error codes. Some places still randomly stick a probe up your tailpipe but rarely.

So I had a thought I have wanted to try a swap with a 1.9 liter TDI diesel out of a VW Jetta, but it is not legal in UT (only swaps allowed are engines that were offered factory in that year). So I think since both are OBD II engines that if it was wired correctly that you could swap the diesel in and as long as you weren't throwing any codes and used the ECU from the VW it should "pass." Honestly even if they did stick a probe up the tailpipe it would still be clean enough to pass that test too.

Normally you get your average "don't care" 18 year old kid running the tests anyway, and most technicians wouldn't hear the difference in the motor unless really paying attention. It also wouldn't look too out of place under the hood like a V8. So really the only thing holding me back is what would the tech get when they connected, and finding someone good enough with the wiring to merge the wiring harnesses without error codes.

So anyone out there who knows the OBD II well enough to know if it is feasable to fly under the radar?