Set up a couch mode match from the multiplayer menu. Make it a 'Deathmatch' and set the turn time limit to 20 seconds on this menu.
When selecting the color of your Shogun press
and you can select a 'Hot Seat' opponent. Basically that means you can control both sides with just one controller.
Have the enemy general run right up to your forces, then pound away the next turn, and pop! goes the trophy.