An improved system to affect alliances

I generally prefer to play with less hostility (I predominantly play singleplayer by the way.) and so I was very glad to see the improvments to the diplomacy system, that I think is one of the better one for these types of games. However, one thing that became somewhat disappointing to me was the fact that there was no way to really get another faction to leave an alliance once they had joined it. I will try to give an example.
I played as the Lumeris and invited one other empire to an alliance, and eventually, the alliance was maxed at four players in an eight player game. Due to the quest where the factions battle for the Academy and the Lost, me and one alliance member ended up on different sides, while the other two stayed on the same as me for the matter of the quest. They were blocking the systems you are supposed to orbit so I had to declare war on them. Which then lead the other two factions to join in. The game ended with me siding up with the other four factions that were our enemies before. It would be nice to have some way to try and bribe/persuade factions from leaving an alliance. The Total War games have a system that works okey for this. Anyone else got thoughts on this?