Wouldn't this be technically possible?
You can set the active car with an app, you can have the app count (but this might be inaccurate). Or you could have an app with a shortkey, say "A", a list of car numbers in the order you want, a piece of paper with the timestamps and at each timestamp you could press A?
I'm not entirely sure why that would be a good idea as it would require a one take no mistakes recording session with a lot of figuring out before hand, while you could easily record in takes during the figuring it all out.