Disable writing to "portable media player"

view story

http://serverfault.com – I need to disable windows machine in the domain from copying files to one's own portable devices. I found a setting that will tell the registry which will tell the computer to 'writeprotect'(StorageDevicePolicies\WriteProtect) portable storage devices. However, smartphones are found to bypass the setting by presenting itself as a portable media player. How shall I block that too? (HowTos)