You can have a leader hold for a number of turns then retreat. Just (No army) Elephants geared towards the rearmost will run for the back of the army trampling; then when their morale fails, run backwards through the middle of the enemy trampling more. You rarely lose an elephant unless he gets caught by webs or vines.

If that commander is a Priestess of Arco you can have her cast sermon of courage to get another round or two out of your elephant or you have one sitting in your retreat province they can heal them and have them do another go next turn. Free attrition.

At least thats how I've tried to get my mammoths to work.