make network time machine - http://hints.macworld.com/article.php?story=20110808120424119

maketc.sh

# /bin/bash
#
# Makes a sparsebundle and set it up

hostname=$(hostname)

# create sparsebundle
hdiutil create -size 300g -library SPUD -fs HFS+J -type SPARSEBUNDLE -volname "Backup-${hostname}" "${hostname}.sparsebundle"

# enable unsupported volumes
defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

echo "copy ${hostname}.sparsebundle to the networkdrive,
open it and set it as the destination in time machine. Or use:

$ sudo tmutil setdestination -p /Volumes/Backup
"