Preheat oven to 375°.
To prepare shortcakes, lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (through salt) in a large bowl, stirring with a whisk; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Combine buttermilk, juice concentrate, and 1 tablespoon vanilla. Add buttermilk mixture to flour mixture; stir just until moist. Turn dough out onto a lightly floured surface; knead dough lightly 5 to 6 times. Let dough stand for 10 minutes. Gently pat dough to a 1/2-inch thickness with lightly floured hands. Cut dough into 10 (2-inch) squares. Place dough squares 2 inches apart on a baking sheet coated with cooking spray.
Combine 1 teaspoon water and egg white. Brush egg white mixture over dough; sprinkle evenly with 1 teaspoon sugar. Bake at 375° for 13 minutes or until golden. Remove shortcakes from pan; cool on a wire rack.
To prepare filling, combine 1/4 cup juice and cornstarch in a small saucepan over medium-high heat; bring to a boil. Cook 1 minute. Remove from heat, and stir in 1/4 teaspoon vanilla. Combine orange sections and pineapple in a medium bowl. Drizzle cornstarch mixture over fruit; toss gently to combine. Cover and chill.
Split the shortcakes in half horizontally using a serrated knife. Spoon about 1/4 cup fruit mixture over the bottom half of each shortcake; top each serving with about 1 1/2 tablespoons whipped topping, about 1 tablespoon toasted coconut, and the top of the shortcake.
When mixing the dough for shortcakes, use a light hand and work quickly for the most tender cakes. If the recipe calls for kneading the dough, knead lightly only a few times so the dough doesn't become overworked.
Use a serrated knife to split the shortcakes. It will cut through the cakes without crumbling them.
You can bake the shortcakes up to a day ahead. Cool completely, and store at room temperature in a large zip-top plastic bag. To reheat, wrap in foil and heat at 350° for 10 minutes.
To freeze shortcakes, cool them completely, place in a heavy-duty zip-top plastic bag, and freeze up to two months. Thaw at room temperature, then reheat as instructed above.