There is a special kind of EZ Pass called an EZ Pass Flex:
Note the switch: if you have over the HOV number of people (either 2 or 3), you flip the switch into the "HOV" position.
The trick is to know how they determine people are attempting fraud when flipping that switch.
I believe they use police on the ground for that purpose.
Houston uses a gang of metro cops at the exits. Every morning they had a long line of people pulled over blocking traffic at the exit ramps from the HOV lanes.
I’m out of that mess for the rest of my life. Yippee!
If you use the HOT lanes with two or more people (three or more on I-95) you order an EZ-Pass transponder that has a switch. When you have the required number of people you switch it so it tells the sensors you are riding free and if you are alone you must place the switch in the toll position and then pay for your trip.
There are cameras that are used to verify compliance. I am not sure if the police patrols have receivers that can tell if you are driving illegal or not.