Make sure that the friendly AIs with you have more cities with the religion than enemies. Convert only one city per not friendly civ and make it a small city. That will control how many votes they get in the end. You will need I believe 75% of the vote for AP victory and you can't account for that 75% by yourself. Also I don't believe it will let you vote for victory if you have too much of the total percentage. So review, build AP or get voted as the leader, have religion in all your cities (also if it is your state religion each vote counts more like twice or non members only count half, its one or the other not both) spam the religion in a FRIENDLY civs cities because they will vote for you, spread to every civ at least one city and make sure only one small city for un friendly civs. That should trigger the diplo victory vote and give you a good chance to win it.