Be up front about it at the beginning of interview. It 1) will relax you (take a giant weight off) and 2) they'll know understand context of what they observe. I have similar fears. My worry is always that people will think my brain is broken and will judge me harshly. I'm all honesty, most people don't actually care. My paranoia has always been around how the secondary behaviors will be interpreted: eyes off to the side, mouth stuck open, neck tension. I'm not nearly as worried about how the words actually sound. Being vulnerable about those fears at the outset goes a LOOONNNGG way to keeping me from freaking out mid conversation. Being more at ease also makes the stuttering less of a problem. That said, it's not easy to be that vulnerable. Make sure you've rehearsed your 1-2 sentences about it before the interview. This helps me quite a bit. Keep your chin up :)