Have you considered melted peanut butter? I'm serious. I was reading a hub by Steveomc about the time he made pancakes with his grandchild. It came to pass that they found they were out of syrup. No more syrup was left in the house, and at that particular time it was not convenient for them to go to the store and pick up some, so they melted peanut butter.
It sounded delicious to me and I think it might work for chocolate cake. Maybe you'd like to mix the melted peanut butter with a little honey.
Good Luck in your culinary endeavors.