Docking stations don't appear as a device by themselves they appear as all the additional devices/ports that they add to a machine. Therefore you need to find something that the docking station provides that otherwise wouldn't be present to identify the presence of the docking station. Perhaps a specific model of network card that can't be present in notebook PCs?
Mark Star - MarXtar LANDesk Enhancements
Home of Power State Notifier & Wake-On-WAN for LANDesk