Stir together all-purpose flour, whole wheat flour, walnuts, baking powder, and baking soda in a medium bowl, and then beat the egg whites with an electric mixer on medium speed in a large bowl until very foamy.
Stir in buttermilk and oil, and then gradually add flour mixture, beating by hand until the mixture is smooth.
Lightly grease a square or round waffle maker, and preheat the waffle maker.
Pour 1 cup of the batter (for square waffle baker) or 2/3 cup of the batter (for round waffle baker) onto grids, and then close lid quickly (do not open lid until waffle is done. Bake according to manufacturer's directions.
When done, use a fork to lift waffle off grids, and then repeat with reaming batter. Serve waffles warm with Blueberry Sauce.
Combine 1 cup blueberries, white grape juice, and honey in a medium saucepan.
Heat just until bubbles form around edges, and then cool slightly.
Transfer to a blender, and then cover and blend until smooth.
Transfer sauce to a serving bowl, and stir in remaining blueberries.