Meanwhile, combine 1-1/2 cups blueberries, sugar and 2 Tbsp. water in large saucepan. Bring to boil on medium-high heat, stirring constantly. Dissolve corn starch in remaining water; whisk into blueberry mixture. Simmer on low heat 2 min. or until thickened, stirring constantly. Remove from heat. Add butter, zest and juice; stir until butter is melted. Stir in 3 cups of the remaining blueberries.