Place the milk and 2 cups of the cinnamon cereal in a pitcher or large liquid measuring cup. Let steep in the refrigerator for 1 hour, and then strain, pressing out the milk with a wooden spoon.
Crush the remaining 1/2 cup cereal and place in a shallow dish. Place a little of the cereal milk in a second shallow dish. Coat the rims of 2 rocks glasses by first dipping in the milk and then in the cereal. Fill each glass with ice.
Fill a shaker halfway with ice and add the cinnamon whiskey, rum cream liqueur and 6 ounces cereal milk. Shake vigorously and divide between the prepared glasses. Use the leftover milk for additional cocktails or serve it without the liquor as a mocktail.