Bullying is an offense not just against the victim but also against the school and society at large, since it disturbs the social fabric. Bullies should be required to speak over the loadspeaker and publicly and sincerely apologize to the entire school, or else face additional suspension or detention (or expulsion depending on their record). If the victim consents to it the bully may include their personal apology along with the public one. Otherwise the bully should have to deliver a separate private apology to the victim and the victim's parents.
This would make a strong statement against bullying, discouraging others from bullying and encouraging the bully to change their overall behavior for the better going into the future so other students will know that they really did change.
As much as bullies are bad and deserve to be 'punished', in no way should we publicly humiliate them. It can sound like a good idea, but in the bigger picture you are bulling them as they did you by forcing them to do something they may not feel comfortable with. I am in no way supporting the act of bulling, but there is no need to do the same to them.