Pour ¼ cup cranberry juice into a shallow bowl and pour 3 tbsp sugar onto a plate. Dip glass rims (6-8 oz. glasses) into juice and then sugar. Set aside.
If you wish to garnish with cranberries, reserve 12. In a blender, place the ice and lime juice (you might have to do this in a few batches) and crush the ice. Add the remaining ingredients and blend until slushy. Taste and add more alcohol or juice if needed. Divide among the glasses and garnish with the 12 cranberries by skewering them on toothpicks and placing on the side of the glass.