Though the focus of this UX Booth article is on how a paired approach to tackling site content can be an improvement to working solo, I think there might be a good, general purpose workshop exercise embedded within.
The suggested approach is to identify a piece of content on a site, and then have pairs of workshop participants collaborate on the solution. After pairs have worked together for a period of time (they suggest 45 minutes, but I think less could work), they’d switch partners in order to get outside feedback for iteration (they suggest 20 minutes). Finally, they recommend each pair presenting their work back to the larger group for a lengthier discussion.
I could see an approach like this working well with large groups, being applied to things like describing and prioritizing user type, brainstorming and prioritizing features, identifying brand attributes and more.