I think the first thing is to manage your expectations. What do you want to have happen? Do you want an abuser to feel bad (how would you know that), do you want them to apologize, do you want them to acknowledge the situation, or admit they were wrong? Or do you just want to let the poison out and doing that you will be able to move on?
I think that expectations in this situation are going to do you harm. All of the expectations I mentioned are contingent on the abuser taking action- which is something you do not have control over. I think the idea of just having the opportunity to have the final say about something could be a way to move on.
The letter idea is a good one as well as phoning/texting someone. If you feel like this is an in person thing that could easily go south if you feel your self slipping into an old role or old reactions. I do not believe that confronting abuse has to necessarily mean confronting the person who did it. Many times the healing we do can be enough. I also do not think you must confront the abuser or abuse in order to heal and move on. There are many times where that could be harmful or counterproductive.
I am a fan of no contact. Its taking your power back and controlling who gets to me in touch with you. It means that contact is on your terms and you control it. It may not be as satisfying to have no contact without being able to say why but the bottom line is the effect is still the same and you have preserved your feelings.