Combine sugar and cornstarch in a small saucepan. Gradually stir in milk and egg substitute. Cook, stirring constantly, over medium heat until mixture comes to a boil. Boil 2 minutes or until thickened. Remove from heat; stir in cre@Sme de menthe. Let cool; fold in whipped topping.
Spoon 2 tablespoons custard mixture into each of 2 (6-ounce) parfait glasses. Sprinkle about 1/2 tablespoon graham cracker crumbs over each custard mixture; repeat layers, using remaining custard mixture and crumbs. Garnish with candy, if desired. Cover and chill.