Connected users notification on shutdown Lion Server

Hi,

My Lion Server on Mac mini server is setup to shutdown himself at midnight and power up and 7 a.m. Sometimes some of my familly put to sleep their Macs so they are still connected to my File Server (they are in idle) so my server can't shutdown becouse system is showing up notofication about connected users. Is there some way to force the shutdown process? Don't want to vnc into my MmS to shutdown it manually.