This guide will work for ALL difficulties.
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. Now 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.