Think of it like the needle on a record skipping. For me coughing or using a phase like "whats it called" or something to break up the initial sentence helps sometimes. But I got to ask why is it so bothersome for you when you're not directly dealing with it? Even if hes like "radio" I never understood how its that painstaking to talk with someone with it. Granted yeah I have a stutter too but still. Either way just understand he doesn't choose to do it and if he could he'd stop in a heartbeat.