Eye contact and a confident posture are a couple tricks that might work for you. Don't feel like you need to answer a question immediately; it's okay to take a few seconds after they answer a question to start speaking. Also, don't be afraid to just be straight up with the interviewer and tell them you have a stutter at the beginning of the interview. I've found that if they know I have a stutter, I don't have to put mental effort into trying to hide it.