We’ve published a KB for using access-based enumeration together with DFS Namespaces. Access-based enumeration makes visible only those files or folders that the user has the rights to access. When access-based enumeration is enabled, Windows will not display files or folders that the user does not have the rights to access.
It takes some tweaking to make this work in a namespace. The KB (907458) also provides a link to download the ABE tool.