I'm also using C4DF + EUI and it works well, you just have to delete the DiploCorner, DiploList and TopPanel-files.
Which leads to my feature request:
When I delete the DiploList.lua, it does no longer show the vassals of other players (at least I believe it is shown there when you don't delete the file).
So would it be possible to introduce a neutral diplomatic modifier that shows the vassalage-status to other players in the diplo-tooltips? Something like
They are the voluntary vassal state of Rome (0)
for example?
Maybe you could even expand this feature and make the modifier depend on their master's attitue towards you, so when the master hates you the modifier will be negative and when you are friends you'll also receive a diplomatic bonus with the vassals?
But this is just an idea. The neutral modifier would be very helpful already.