Did you try disclosing your stutter? Being open about it in the interview can actually help reduce the anxiety around your stutter. If people know that you stutter, then they know what to expect and you don't have to feel bad about when it does happen. I find that the more I see the other interviewer as being understanding about my stutter, the less pressure I feel to be fluent. This makes me stutter less since I don't have that added anxiety of being found out.