When you have a moment with him that's 1 on 1, talk about his stutter with. Make it light hearted convo but take it serious, if that makes sense. This convo could help him relax around you in the future and possibly make him stutter less. One pet peeve of mine is people who say they themselves use to stutter or their cousins does or something. If you actually did use to stutter or know someone keep that to yourself, maybe wait to tell him later. Because it feels like Everyone says they stuttered and it's irritating lol Ending up not really trusting them thinking they are full of shit. Group sessions with him should be kept limited. Yes he still may have a job to do but how much talking does people really gotta do anyway? Most meetings are time wasting BS anyway