Umm I dunno that is hard. If you can muster the courage I'd say just speak up even if you stutter. Group interviews must be looking for the person that stands out. If you can Be friendliest most out going person in the group you'll get past the group interview. Ask people questions about themselves. Force yourself to talk to eveyone. I have a very well rehearsed and up beat "hi how are you?" For approaching customer service people and new people. I almost always get a positive reaction and it removes alot of the tension so I stutter less and I've already got them on my side so even if I stutter they are more receptive. If you can get something like that going you'll be ok