Your situation is very similar to mine about a month ago. I wasn't out to my department either, but I had to present my final thesis to the entire department of professionals and students. They would introduce me with my girl name, while T had changed my voice and appearance too much. I couldn't even pass in girl mode anymore, even if I wanted to.
Not sure what DADT means, but a mail sounds appropriate. Tell the person who will announce you to announce you with your chosen name. He or she may not agree with it, but he or she should also not ignore your wishes. My professor had no issues with it at all, immediately changed my name, told the person who would introduce me to use my chosen name and no issues were had. I hope you will be given the same treatment.