I say make a centralized server with an antivirus; for sake of example lets say the AV is ClamAV, you make a small python script that allows users to send files to that server to be scanned(over a LAN), the server returns a boolean value(true or false) true meaning there is a maleware, false meaning its clean, and if there is a virus found have the client script unmount the drive, log the event, and maybe even set up a realtime notification system. Also set up a network gateway that scans incoming packets from the network. If you don't know python or any other scripting language i suggest you learn, ever good admin has a script language and knows his *NIX.