Google Analytics accounts have access to event tracking by time, so you can use the following hack in order to get real reports of bounce rate without skewing any of data. Even more, the hack will help Google Analytics track better (not perfect though) the time spent on site by each visitor.

What you need to do is to fire up an event each time a user spends more than 10 seconds on the website. Just add the following line under the pageTracker._trackPageview(); line:

setTimeout('pageTracker._trackEvent(\'NoBounce\', \'NoBounce\', \'Over 10 seconds\')',10000);

Update
In case you have decided to already update to the new code here is how the hack would be applied (place it as the last _gaq.push declaration) .

setTimeout('_gaq.push([\'_trackEvent\', \'NoBounce\', \'Over 10 seconds\'])',10000);

10000 refers to the number of milliseconds after which you want to fire up the above code. If you want to do it after 15 seconds than you need to place there 15000.The hack will not alter your data in any way. It will just record in the Events section all the non-bouncers.