Combine the dates and ⅓ cup water in a small saucepan, and simmer over medium-low heat for 10 minutes or until tender. Drain, reserving the cooking water. Place the dates in a blender, and purée until smooth and creamy, adding cooking water, as needed.
Combine the onion, celery, and bell pepper in a large skillet, and cook over medium heat for 7 to 8 minutes, stirring occasionally and adding water, 1 to 2 tablespoons at a time, as needed to prevent sticking. Add the garlic; cook for 1 minute more, stirring constantly. Stir in the wheat berries, tomato purée, date paste, ketchup, and Worcestershire sauce. Cook for 10 minutes or until thick, stirring occasionally. Season with salt and pepper. Serve in buns.