I was wondering if anyone's tried this and how well it works out:

For a 5-player game, set up the map as a 5 by 5 grid with four civilizations on the corners (one each) and the fifth in the center. The corners orient their tiles as coming from either edge of the map, but the center can choose any orientation.

That's the same one we've used in my group several times, seems to work fine. Though there is a little problem with some of the fast and warlike Civs like Mongols being in center spot. Otherwise it doesn't have any obvious problems and is easier to set up.

Our 3 player and 5 player maps are formed so that each player gets 3 map tiles + their own nations map tile. Then those are arranged in 2x2 grids that touch each other at the bottom corners. That means, that in a 5-player game, the map has a star shape hole in the center. When traveling the map, the edges of the 2x2 map tile grids match well enough that the map is easy to travel. And it's balanced since everyone has the same amount of space around them. It feels like playing on the surface of a sphere. Same thing also works well for 3 player games.

Another way to think about this is to make the map like the 4 player setup and then spread it to get the fifth player 2x2 tiles in or take 2x2 tiles out for 3 player game.