The obvious gender difference should make it straightforward for your dad to beat the rap. I assume he doesn't want to schlep down to LA to appear in court. So a carefully-written TBD would have to do. I would suggest keeping the TBD very short. Just say not guilty, the evidence clearly shows that the defendant was not the driver. It can't hurt to mention the gender difference. A photo from his driver's license along with a copy of the ticket photo should complete the case for dismissal.
It's not clear to me that you can do a TBD without "testifying". Once your dad testifies, he may be compelled to identify the driver. That's something to check with someone more experienced. If it were me, I'd word the TBD carefully to avoid the appearance of testifying, i.e. avoid making statements such as "I wasn't the driver."
Good luck to both of you, and watch those one-eyed bandits from now on!

