Stir together sugar and boiling water until sugar is dissolved. Stir in cold water, lemon zest, and juice. Pour into ice cube trays, and freeze until solid, about 8 hours.
Process 2 cups frozen lemonade cubes, blueberries, and vodka in a blender until smooth. Stir in chilled club soda. Pour into glasses; garnish with lemon slices. Serve immediately.