Pour 4 cups of the chilled coffee into two ice cube trays. Freeze about 3 hours or until firm. In a large pitcher combine the remaining 1 cup chilled coffee, the root beer, liqueur, and vodka. Cover and chill until needed.
To serve, add the coffee ice cubes from one tray to root beer mixture. Pour root beer mixture into small glasses over the remaining coffee ice cubes. Drizzle with half-and-half (if desired) and garnish with lemon peel twists.