This is extremely hard to do and I understand, but I like to start out job interviews by politely saying something along the lines of, "Before we begin I just wanted to let you know I do have a mild speaking stutter so if I stumble at times please just let me work through it. I've prepared a lot and am very excited for the opportunity!" A lot of employers love the honesty and making them aware of the situation clears the air and makes me more comfortable. Don't let this keep you down and keep focusing on the positive!