We have a Good To Go! program in place just for vehicles like yours. The program requires you to have your vehicle verified at one of our three walk-in centers, equipped with a license plate pass that is registered with the program, and tested to ensure it is in operational order.
If you travel as a carpool trip, you can avoid the toll by contacting the Customer Service Center within 45 days from your HOV-eligible trip to get the toll refunded to your Good To Go! account. I recommend this option rather than holding a Flex Pass out your window or through your sunroof.
Vehicles with metalized windshields are indeed a challenge area in the toll industry for select vehicles, and we have researched what other toll agencies are doing in this regard. We found that in Washington DC very few vehicles are involved and they have put in place a similar approach to have a driver call for HOV trips to be removed from their account. We plan to operate in this manner on I-405 for an interim period to assess how many drivers are affected. We are also investigating a mobile app or process similar to what Atlanta or Miami does to declare the trips to be made in advance which will be HOV and should not be charged.