We have launched a similar website, currently in beta: http://www.zombal.com . Maybe, just maybe you can start using your secret lab in the coming months.
Looks very interesting. I'd suggest that you offer as much feedback to losing submissions as possible (see my other comment), to help losers improve and keep them interested in trying other challenges.
Zombal has a different format from Innocentive. The way it works is someone (the launcher) launches a task (usually scientific) and sets a budget or approximate payout amount. Then several people (the catchers) bid on it, they don't do any work until they are actually hired to complete the task.