Hi,
not quite sure, if you can do this in the jabber-config.xml. I think you need to put these information into the configData.properties and the userData.properties you can find in the %appdata%\Roaming\Cisco\Unified Communication\Jabber\CSF\Config directory. (See screenshots attached)
We are pushing these files to the clients via GPO.
Hope this is what you're looking for.
Cheers!