While I don’t have an answer for you, I do have a feature request out there for the exact same thing. https://forums.fogproject.org/topic/6014/create-the-concept-of-a-foreignmasterstorage-deployment-node
Right now there the only way to do this is manually or scripting via sql dump and sql import of the images and snapins tables between the deployment nodes.

You can do something similar but with storage nodes (not a master deployment node), and you will need to install the /tftpboot files on the storage node. You will need to use the location plugin and storage groups.