Combine first 3 ingredients in a large saucepan. Gradually add broth, stirring constantly with a wire whisk. Bring to a boil, and reduce heat to medium. Cook 3 minutes or until thickened, stirring constantly. Remove from heat; stir in buttermilk and Parmesan cheese, and set aside.
Place the corn and onion in a food processor, and process until corn is coarsely chopped. Combine corn mixture, egg whites, and egg in a large bowl; stir well. Stir in cornmeal mixture, 1/4 teaspoon salt, and peppers. Pour polenta mixture into an 11 x 7-inch baking dish coated with cooking spray, spreading evenly. Bake at 400° for 50 minutes or until browned. Let mixture cool. Cut corn mixture into 20 decorative shapes with a 1 1/2-inch cutter. Remove shapes from baking dish, and arrange on a baking sheet coated with cooking spray. Discard remaining polenta mixture. Bake at 400° for 20 minutes.
Combine nonfat cream cheese, yogurt, grated lemon rind, and dash of salt in a small bowl; stir well, and set aside. Spoon about 1/4 teaspoon cream cheese mixture onto each polenta cake. Top each cake with a salmon strip, and garnish with fresh dill, if desired.