Preheat oven to 375 degrees. Line a standard (12-cup) muffin tin with paper liners; coat liners with cooking spray.
Whisk together cornmeal, baking powder, baking soda, salt, and 1 cup flour. In a large bowl, stir together bananas, buttermilk, rice syrup or honey, lemon juice, egg, and vanilla. Fold cornmeal mixture into banana mixture just until combined. Toss blueberries with remaining 2 teaspoons flour, and gently fold into batter.
Spoon batter into prepared tin, filling to the brims. Sprinkle each muffin with sugar. Bake until a toothpick inserted into center of 1 comes out clean, about 30 minutes. Let cool completely in pan on a wire rack.
Muffins can be stored in an airtight container at room temperature for up to 3 days.