What about a video game tournament? Madden, or whatever the latest craze is. It would be two tournaments, players vs players, fans vs fans. Winners face off.
There would need to be some type of qualifying tournament for the fans, to narrow it down to the same number of players. Someone smarter than me would need to figure that out..or just do a lottery?
Treat the event like a Comic-Con. Have different rooms for Q&As, autographs, vendors, etc. (Andre Reed in Hall H @3PM for Q&A. Tickets required to get in, priced dependent on star power). Last Q&A would be in the highest capacity room with Josh.
If a fan wins the tournament, have that person on stage with Josh for the closing Q&A.
At the end, have a few of the consoles used in the tournament autographed by the players that competed and auction off for charity.