Solution
Symlabs Virtual Directory Server and LDAP Proxy support the option to store additional data attributes locally for any entry in a directory server. It does this by filtering requests and storing the additional data locally on the file system, where Virtual Directory Server is running, or optionally, in another directory server or relational database. This is fully transparent for the application: From the application's point of view, it appears as if the additional data is stored in the directory, even though Directory Manager is managing it locally.