As far as I know and am able to research right now, there is no way to work around the limitations of the various browsers that do not support the file:// protocol. You would have to include some 3rd-party addin / applet or other sort of component that may provide such features. Personally, I don't know any such addins since this is not a use case most people use a web application for. Normally, a DFS tree is used as a single, unified entry into multiple shares.
Alfresco specifically has not been designed to provide access to files that are not managed in its own structures, so this use case has received no attention in any of the product development.
