This is one of my older mods that I have altered to work with DeI. It will unlock all the diplomatic options (confederate, client state, satrapy) for all factions.
Download: http://www.mediafire.com/download/lk..._Dipl_DeI.pack
or
Steam Version: http://steamcommunity.com/sharedfile.../?id=350391545
This submod is now also available as part of the DeI Official Submod Collection on Steam.