This doesn't really seem like rational self-interested behavior on the part of the students. There are thousands of doctors trained every year in a country as large as France. A student's choice to mean or nice to the tiny subset of his peers which he will have substantial interaction with is going to have a negligible effect on the average score. Therefore, it's very much in his interest to cooperate with his small group of local peers in order that the group can do better than the average.

Since students do end up being nasty to each other, that tells us there's something very irrational going on. Thus, it might be more effective to try to manipulate that irrationality away than changing the fundamental structure of the tests.