Been there. It sucks. I once had a guy straight up stand up and leave a talk I was giving as part of a job interview. I know it sounds crazy, but it might help to talk about it right at the start of the interview. I suspect you worry that they'll see you stuttering for days and weeks beforehand and THROUGHOUT the interview. If you just give a disclaimer at the beginning, or make a joke about it, you take the control from them. Whatever approach you take, practice the line beforehand. Good luck!