A while ago I wrote a proof of concept tutorial for turning a Windows server into a FOG storage node. https://forums.fogproject.org/topic/6941/windows-server-as-fog-storage-node-proof-of-concept-blog
You can not add additional space to your fog server by sharing disks on another server. This method is asking for problems. But you can turn another server into a FOG storage node (so to speak). By using a fog storage node and a the fog location plugin you can train all of your computers to image from the storage node instead of the master node.