From the Single player menu, choose "SET UP GAME", and then go to "Advanced Setup". Make sure the Victory Condition for "Time" is on. Under the "Advanced Game Options" box, turn on the "MAX TURNS" option and set the number in the box to 1. Now either add or remove AI players until it's just you and 2 AI players. Set one of them to be on the same team as you. After you've chosen whichever leader you want to win with, simply start the game, create a city, and end your turn. The combined total of you and your teammate's score will outrank the other AI player and give you your victory. After you've exited to the main menu, just choose another leader and repeat the process. Once you've done this with all the of base game leaders the achievement will unlock. This also works for all DLC leaders as well.