when a civilization is losing could it agree to become your satelite empire. From then on would the following be true for that empire:
-It has and generates your influence/culture, this also means that it's cities are save from flipping to the master empire because it has the same culture.
-It does no longer have an idependent foreign policy. Instead does it have the foreign policy of the master empire.
-satelite empires always have the same form of government as the master empire.
-When all non satelite empires are defeated or are alies have both the master empire and the satelite empire won(thought the satelite empire could be given a score penality because winning as a satelite empire isn't the same as a normal victory)
-You can still trade with them like before.
-You can't declare war against a satelite state without declaring war against the master empire.
This could allow you to create a buffer of satelite states around your empire with who you could do trade knowing they shall never attack you(expect maybe some very rare events).