Collect odd tidbits of information about the community members and then see who can guess who did what.
For example, Interesting facts or accomplishments.
You can use the poll feature to have direct feedback from your event participants, see the temperature level... of course it implies that your participants have live access to their accounts, smartphones and wifi being essential!
How about a version of the Darpa Red Balloon Challenge? It might be a bigger event than what you were thinking, however, but it would get them engaged, having fun and using Jive (as they report back into it).