I suggest that rewards for not crying is NOT the way to go. He has an emotional issue that needs to be addressed. He needs to learn that leaving you at the door is the way to go. I also suggest that you walk him to the door, give him a quick hug and immediately leave. The teacher will attend to him. The longer you linger the more difficult it will be for him to make the break.
If the teacher is planning to do something such as having something for him to do as a reward, that may help but giving him some trinket is not helping him to let go. You want to teach him that getting ready for school and leaving you are things he can do for himself because he will manage his feelings. You don't want him to do what is normal in order to get a trinket. You want him to learn how to manage his feelings.
Peer pressure will also help. I wouldn't worry about being teased. Let the teacher handle that aspect also.
I suggest that you're giving too much emotional and physical attention to your son's clinginess. Be matter of fact, drop him at the door, give him a quick hug and leave. At home that night ask him about his day but don't emphasize his reaction to being left at school. Let him know that it's OK to be sad and that you know he'll eventually figure out how to let go. You help him let go by leaving and not focusing on the problem.