Combine the first 3 ingredients in a medium saucepan, and bring to a boil. Cover, reduce heat, and simmer 10 minutes or until liquid almost evaporates. Add sugar and lemon juice, and cook over medium-high heat for 8 minutes or until slightly syrupy. Place the pineapple mixture in a blender; process until smooth. Pour the mixture into a bowl; cover and chill.
Reserve 1/4 cup of chilled pineapple mixture. Fold the whipped topping into the remaining chilled pineapple mixture. Spoon 1/2 cup of the pineapple mixture into each of 6 glasses, and chill. Top each serving with 2 teaspoons of the reserved pineapple mixture before serving.