Well I just want to say that the game was unwinnable by Diplo victory, Joao II's population is so high that it will always be a stale mate. (everyone else was voting for me but his population was high enough that it was still a stale mate)
However, I did start up a OCC on a Tiny Islands, High Sea Level, Archipelago map a few hours ago just to mess around and...
It was tough. The person I was running against kept changing. For a while it was Qin Shi Huang and ending in stale mates each time as a few of the leaders didn't like me, then Gilgamesh started to run (he was my best friend in the game so this did not make me happy) and then pretty much every leader except for Isabella was Friendly with me (Isabella was constantly changing from Annoyed to Cautious with me, and was pretty much hated by all), but it was still ending in stalemates as Mehmed II kept not voting.
And then FINALLY I ran up against Mehmed II. All of the leaders began to vote and walah, the German City State of Berlin became the capital of the world and I had won a Diplomatic victory!
P.P.S. I also passed most of the other resolutions while hoping that Qin Shi Huang and Gilgamesh would lose population. I passed the No Nuclear Profileration, the One Currency, the Trade Routes for every city, the Environmentalism Universal Civic, the Emancipation Universal Civic and I think that's all. I couldn't pass Universal Suffrage and Free Religion because that stupid Isabella kept defying them.
P.S. I hate tiny islands maps, espesically with high sea levels.