Crust: Mix graham cracker crumbs, sugar substitute, and melted butter. Press into an 8x8-inch pan. Chill.
Filling: Beat cream cheese, powdered sugar, and vanilla until smooth. Fold in light whipped topping.
Topping: Cook blueberries, sugar, lemon juice, cornstarch, and water until thickened. Cool slightly .Spread filling over crust, top with blueberry mixture. Refrigerate for 4 hours until set. Cut into bars and serve.
This makes 12 thick bars. Each bar on WW is 7 WW Points.