In a small saucepan, combine the sugar and cornstarch until evenly blended, then stir in the blueberries, water, and cinnamon. Bring to a boil over medium heat and simmer until slightly thickened. Remove from the heat and stir in the juice. Spoon into a heat-proof glass bowl and serve warm or cover and refrigerate for up to 1 week. Reheat in the microwave on medium power for 45 seconds or on the stove over low heat.