That is a good idea and likely to pay off far faster than my idea of see who does not send in a June payment.
I have not lived in "OC" / SOCAL" for many years. So, I am no longer familair with what lanes are toll or how they work.
Expanding on your idea, it might be able to trace the likely point the car entered into the freeway, then moved into the HOV lane- which is usually done at first opportunity.
So, ideally, car is in toll lane and they have a transponder. Identify where they entered the toll lane, then look at the ramps between that toll lane and the previous toll lane (for a moment, presume they did not miss a chance to get into a toll lane).
Then.... hit all commercial and red light type cameras around the likely on ramp possibilities for the car. Here's hoping that they have a toll tag!