He shouldnt have a problem. I've ridden this ride several times and the only problem I've ever had was at the end, when the shoulder harness didnt release and the CM had to come over and push down on it.
Everyone was so worried about running off to their next adventure that no one noticed and it wasnt embarrassing at all. The front seats of the cars have more room than the back, but honestly I cant remember where I sat.
Have Fun!