I (usually) mention it up front to take away my worry that when I stutter the first time they won't know what just happened. Yes, this does not give them any opportunity to talk ask questions about it, but I'm my experience most interviewers don't know what to do when you tell them you stutter. They just don't know what to do with this new information. So, I just move on. I think its a pretty personal thing, so this is how I approach it. If you find it is a way to let them ask questions about it, that's awesome. I may bring it up later if they ask about my skill/willingness to give public presentations, but I have never had an interviewer ask me about it. They are probably afraid of a discrimination lawsuit if I don't get the job.