I usually start with "just to let you know, sometimes when I am nervous, I stutter" -especially if I am having a bad stutter day. That's always worked for me. At least they'll give you time to get your words out. I also focus on something in the room, like a cupboard or a chair and focus on the outline of it as I am talking. That tends to help me calm down and not think about the words I am saying. Good luck