Combine sugar, corn syrup, and lemon juice in a medium saucepan; stir in blueberries. Bring to a boil, reduce heat, and simmer 3 minutes or until berries pop. Strain mixture through a sieve into a small bowl. Discard solids.
Combine cornstarch and water, stirring with a whisk; whisk into blueberry mixture. Bring to a boil, and boil 1 minute. Cool completely.