It's pretty impossible for that thing to work on a Prius - the Prius doesn't have an alternator. It has two generator/motors (MG1 and MG2) that are sometimes generating power and sometimes driving the wheels or starting the gas engine.
The 12V battery system for the gas engine's ignition and the car's accessories is run and charged by a DC/DC converter off of the big drive batteries in the back of the car, rather than an alternator.
The Prius has a cool system from an engineering perspective... too bad the resulting car is so lame!