Preheat the oven to 250 degrees F. Place the cookie sheet in the oven.
In 1-quart saucepan, combine water, cornstarch, 1 1/2 cups blueberries, and 2 tablespoons sugar, and heat to boiling over medium heat, stirring occasionally. Boil 1 to 2 minutes or until the berries burst.
Remove from heat; stir in lemon juice.
In a large bowl, combine flour, baking powder, baking soda, salt, and remaining sugar. Stir in buttermilk, butter, and eggs just until flour mixture is moistened. Stir in remaining berries.
Lightly grease griddle or nonstick 12-inch skillet; heat over medium heat until very hot.
Drop batter by 1/4 cups onto hot griddle, spreading batter gently to make 4-inch rounds. Cook pancakes 2 to 3 minutes. (Pancakes are ready to turn when the batter begins to set, bubbles start to burst, and edges look dry.)
Turn pancakes over, using a wide spatula. Cook 1 to 2 minutes longer, until puffy and undersides are a rich golden brown. Transfer pancakes to a cookie sheet in the oven; keep warm.
Repeat with remaining batter, greasing griddle if needed. Serve pancakes with blueberry sauce.