If we have a shared war we can always open borders. We could bribe Mehmed on Church before we declare on Mehmed, then Church will open borders. According to diplo we should be able to bribe Mehmed on Roose as well, but currently he says he would have nothing to gain. I do not know what that response means or if it is likely to change.
Another crazy "let's change everything" idea.
What if we didn't steal CS from Toku and instead used him as EP gift city target. We can also get OB with him if we bribe Mehmed on him before declaring on Mehmed. In my test yesterday we got to 71854
with one more succesful spy mission. The EP we planned to used to steal CS would allow that 45th spy mission. If we can get a total of 73500
, then we'd need one less wonder. We wouldn't have Bureau, but we would need one tech and one wonder less. Bureau hammers and commerce are for sure not enough to make up for Engineering and ND. Shouldn't forget high upkeep cost of Bureau either.
Oh wait.. We'd need to get Toku somehow into another religion first for this to work. Requires a missionary other than Tao. Could be challenging.
Mehmed's Jan will teleport when we declare on him. It is no threat to gift city.
Correction: Getting another religion to Toku isn't that hard at all. Give him some European city we've just captured, which is still in revolt. Weird that he is still Confusian despite not having any Confu city. He should switch religions immediately when he receives a city with religion.