energysaver prefs

Hi all, nice challenge: when a computer is in use (not at loginwindow) we don't want it to go to sleep. when a computer is not in use (at loginwindow) we want it to go to sleep after 30 minutes. this can easily be done using login- and logouthooks doing a pmset blabla command. extra challenge is that we want to wake all the computers at 06:00 AM. this can easily be done using MCX or placing the right com.apple.AutoWake.plist in /Library/Preferences/SystemConfiguration. BUT waking up several 100 computers at exactly the same moment can't be good for our power infrastructure so i'm searching a solution to wake the computers at random between 06:00 AM and 06:05 AM. any ideas?