Place the frozen blueberries in a microwave-safe bowl. Microwave for 1-2 minutes, or until plumped and slightly warm. Pour the blueberries into a blender and blend on highest setting for 1-2 minutes, or until a super-smooth puree forms. Use the back of a spoon the press the puree through a fine-mesh sieve. It may take a little doing, but you should be left with 1/2 cup blueberry juice in the bowl and 2 tablespoons or so of blueberry pulp in the sieve. Mix 1/4 cup of the water with the blueberry juice. Pour the blueberry juice into a small saucepan and heat until boiling. Meanwhile, stir the gelatin into the remaining 1/4 cup water and let sit 1 minute. Remove the blueberry juice from the heat and stir in the dissolved gelatin and the maple syrup. Pour into a glass loaf pan or molds of choice and chill 1-2 hours. Cut into desired shapes.