Combine first 8 ingredients in a bowl; stir well. Combine buttermilk, egg substitute, molasses, and 2 tablespoons melted margarine in a bowl; stir well. Add to flour mixture, stirring until smooth.
Melt 2 tablespoons margarine in a 9-inch cast-iron skillet. Stir in 1/3 cup brown sugar; cook over medium heat 1 minute. Remove from heat; sprinkle with walnuts.
Peel and core pears. Cut each in half lengthwise. Cut each half into thin slices, cutting to, but not through, stem end. Fan pear halves; place, core sides up, on top of brown sugar mixture in skillet. Pour batter over pears; bake at 375° for 35 minutes or until a wooden pick inserted in center comes out clean. Let cool in pan 5 minutes on a wire rack. Loosen cake from sides of pan using a narrow metal spatula. Invert onto a cake plate. Garnish with cinnamon sticks and pear slices, if desired.