The way he got 200 MPG was he added a whole bunch of batteries to his car. The Prius can run up to in town speeds with it's Gas engine completly off running its electric motor alone. With all the batteries he added his gas engine wasn't having to came on till he had gone a long way on them. He also rigged his so he could plug it up at night to charge all the batteries. I would like to see the MPG results of his car if he charged up it up and then struck out to New York City and didn't plug it up anywhere along the way. I bet they would be very different indeed. You couldn't rig up a Insight like he did because it can't run on the electric motor alone and if it could it probally wouldn't go very fast maybe 10-15 MPH because it's motor is only a 10 KW.
Actually, since the Prius can run on electric power only, it can achieve infinite gasoline mileage.
The Insight electric motor is 3 times smaller and is not liquid cooled. Experiments with Mima indicate that the Insight should be capable of around 130 miles per gallon if a larger battery pack was used.
The good news is that the same size "plug in" battery would last much longer on the Insight, so the real world practicality of this modification might go to the Insight. The Insight mod could use a much less expensive battery and still go a greater distance on a charge.