I have an evil-genius 2-step plan on how to fight this.
first, you need to have a small a/v player. hey, smart phones can play audio and video! now, we need a reducer so that we can 'pipe' the video into the camera, optically, to create the illusion that the car is empty (or in any state we want). easy to pipe in audio, simply by putting the phone spkr near the mic.
2nd part of the plan is to edit the contract (adding a section) that says you may, at your option, provide 'performance art' inside the car. something to that effect.
now that you've set it up, have some fun! what could you record that would be great for playback, for them to see? fake a murder? fake a corporate take-over? fake a plot of some kind? some other kind of intentional mis-direction?
you already covered yourself by the performance-art clause. you can laugh it off when you sign their contract and just make a joke about the camera. if done properly, they won't know what you have in mind.
the rest, as they say: 'hillarity will ensue'.
and unless its illegal (its not) to pipe in any video stream you want in front of a spycam, you can do this and mess with their data collection while having some well-earned laughs at their expense.