I was a bit shocked to see a 'PZEV' sticker on a Toyota Camry a couple of days ago, sitting in a parking lot. It didn't LOOK like there were any modifications to the car, nothing obvious at least. I'm thinking someone just put the sticker on. I figure if anything like this exists, someone on this forum would have heard about it.
There is a new magazine at our house, the name of which escapes me at the moment, but it's about new technology cars. In one article about PZEV vehicles, there is a list and photos of each car. You'd be surprised at the lineup. Ford has a Focus with a new ultra low emission engine, Honda and Toyota of course, and VW. The Camry is available with a super low emission engine, 4cyl only I believe. There were about ten cars mentioned in the article, all except the Prius and Honda were conventional ICE machines.
The Camry PZEV has a few mods under the hood. It uses the same HC-Absorbing catylitic converter that's found in the '01-'03 Prius.