He could get used to it.....take him for short rides to build up his tolerance and take it easy on the brake LOL! I had a GSD who used to get car sick as a pup and it got a little better as he became an adult. He learned to lay down in the car and not look out the window when in motion and he would rarely throw up unless I was driving jerky and brake happy.
Short rides to happy places. Lather, rinse, repeat. Keep your driving calm so the dog doesn't get thrown around a lot. Also -- if you're someone who likes loud music, like I do -- keep the music down, off, or on something soothing like classical. I had a dog that used to get motion sickness constantly. So I would load her up and drive just down the street to the park, and there we would have a nice walk together. Or I'd take her to Petsmart, or somewhere else fun. She began to associate the car with awesomeness. The shorter the trip, the better to start with. I had to change a lot of my habits, too, because I drove with a lead foot and blared my music, both of which can stress a dog out.
Persevere. He will hopefully outgrow it if you take steps to acclimate him to the car in a positive manner.
One thing I wanted to add is don't feed or give your dog anything to drink right before taking them in the car. A full stomach can often make it worse and upset their stomach even more. AVA my older dog gets car sick. I usually put the crate in the car when I do take her out just incase she does throw up. It doesn't happen as often mostly on longer trips but it has gotten better as time has passed.
You need to take him more often and he'll get over it. Start with small trips like around the block or to the store a few times a week then make it longer. The more you take them the faster they get over it.