Puree blueberries in a blender.
Transfer to a heavy saucepan, and bring to a boil.
Reduce heat and simmer, uncovered, until blueberries are reduced to about 1/2 cup (125 mL).
Stir in lemon juice and cool to room temperature, In a small saucepan, sprinkle gelatin over water.
Allow to soften for 1 minute.
Cook and stir over low heat until gelatin dissolves.
Set aside to cool.
When the gelatin is cooled, combine gelatin, water, sweetener of your choice, and tofu in a blender.
Blend until smooth.
Pour in milk and vanilla.
Blend until completely mixed.
Add nondairy whipped topping and pureed blueberries.
Blend just until mixed.
Transfer to an ice-cream freezer or a 9 in. (23 cm) baking pan.
Freeze according to freezer manufacturer's instructions or place pan in the freezer and freeze until firm.
Break into pieces.
Place in a large mixing bowl or food processor.
With an electric mixer or food processor, beat mixture until smooth.
Return to the pan and refreeze.