Combine the blueberries and the water in a medium-size saucepan. Partially cover the pan, then bring the mixture to a simmer over medium heat. Continue simmering the berries until they begin to break down, about 2 minutes. Stir in the sugar and cook the berries until they become soft, about 1 to 2 minutes more.
Stir together the lemon juice and cornstarch in a small bowl until evenly blended. Stir the mixture into the berries, then cook them at a low boil, stirring constantly, for 1 1/2 minutes. Remove the sauce from the heat and transfer it to a medium-size bowl. When the sauce is cooled, cover it and place it in the refrigerator to chill.
Line a 9- by 5-inch metal loaf pan with two sheets of crisscrossed plastic wrap, leaving a 3-inch overhang on all sides, then chill the pan in the freezer for 10 minutes.
Place the container of sorbet in the refrigerator for 30 minutes to soften, then spoon the sorbet into the pan and mold it, using a sheet of plastic wrap to smooth the top as needed. Cover it with foil and freeze it for 2 hours. The last 30 minutes, soften the vanilla ice cream in the refrigerator. Remove the pan from the freezer, add half the vanilla ice cream, mold it, cover it with foil, and freeze it and the remaining ice cream for 30 minutes. For the third layer, mix the remaining ice cream with 3/4 cup of the blueberry sauce, and add it to the pan. Freeze the dessert for one more hour.
Chill a platter in the refrigerator for 15 minutes. Right before serving, thin the remaining blueberry sauce with a spoonful of water or orange juice. Invert the dessert onto the platter, unwrap it, and garnish it with fresh berries. Use a sharp knife to slice the dessert, and serve it with the sauce.