It's possible that they "might" drop the charges against him if you do that, and it would be the right thing to do if they really did belong to you. However there's no guarantee that they will since the driver is usually held responsible for the vehicle, it's passengers, and it's contents.
Since he was arrested and not you then I have to assume that the drugs where either hidden in the car or on his person, either way it would be very hard for him to convince the Police that he had no knowledge of the drugs being in the car.
Since he was arrested and not you then I have to assume that the drugs where either hidden in the car or on his person, either way it would be very hard for him to convince the Police that he had no knowledge of the drugs being in the car.