Sessions Being Left Open in Enterprise

We've recently upgraded our Business Objects Enterprise environment to version XI 3.1 SP3. We are on concurrent licensing with not that many licenses. The issue that we keep running into is that whenever a user closes the browser without logging out, the session is being left open. I've reminded our users multiple times but they just forget all the time. This wasn't an issue on older versions.

Is there a way we can kill these leftover sessions? I've looked in various places in the Central Management Console and couldn't find a way to do that.

We are using IIS by the way.