You better teach your little baby to ride in the car without you turned around in your seat like that, because if you get in an accident in the position you're shown in this video you're going to have serious injury or you're going to get killed.
I get really car sick if I sit in the backseat of a car. I wouldn't be able to sit in the back with my kid. They would just have to learn how to sit in the backseat without holding my hand. Why not just give him something to play with, something to occupy his time? I don't believe this is the only way he'll stay calm on the road. He is probably calm with a toy or a book. I bet the mom is the one that started this, and now she realizes it was a bad idea. You're gonna have to stop pacifying him all the time. He is gonna have to learn that he won't get his way all the time, and that he is gonna have to learn how to entertain himself.
A lot of people suggest sitting in the back, which is a fine idea. Also, if that isn't an option, give him a toy or play a game finding colors or animals, or sing songs, tell a story. Giving in to the demand could teach bad habits that are cute now, but not so much when he is 7, 8, 9...or an adult.