I'm guessing the UN is complete, or near so? Get all the AI in a war against the French. Assuming you're #1/#2 and they're #2/#1, you'll most likely get the vote. Yes, you'll get a rep hit for losing the lux (maybe), but it still might work out if you get that AI civ that lost on the deal soon enough. Like that turn.
You might even want to make the MA (I would avoid MPPs) with that civ before gifting the city. With a generous amount of gold, they should probably stay at war and vote for you when the UN vote comes around.
You might even want to make the MA (I would avoid MPPs) with that civ before gifting the city. With a generous amount of gold, they should probably stay at war and vote for you when the UN vote comes around.