Hi Rob,
You can create a custom handler which will synchronize the documents by API (
Synchronization using API) when someone publishes a document in the current version (6.0). See here:
Event handlers for more details about a custom workflow handler. It is also possible to implement this in version 4.1:
http://devnet.kentico.com/docs/4_1/devguide/using_api_to_synchronize_documents.htm
http://devnet.kentico.com/docs/4_1/devguide/workflow_handler.htm
It is also possible to set up the notifications e-mail about publishing and when a document is published, you can access the CMSDesk and synchronize it manually.
Version 7 will have a new feature - Advanced workflows - there will be an easier way how to implement it. It will support custom actions for particular workflow steps.
Best regards,
Helena Grulichova