How about giving him an assignment this summer of getting in contact with the Stanford folks and seeing if he can work out a deal to transfer there in 2 years (well, 3 years). Or maybe trying to find a faculty mentor.
Having the right mentor can open LOTS of doors.
When I got my master's degree - I was offered a full stipend, plus teachings assistantship over the phone. Just by talking to the right person!
Help him see that each choice is simply a path to where is wants to go - not the final solution. Also, maybe have him map out his entire path to being a doctor. Seeing 2 years cut off of a 10 year program just might be the motivation he needs.
You definitely want him to feel he is making the decision, but helping him "find" that decision isn't bad either
