Preheat oven to 350 degree F. In a medium bowl combine the crushed wafers, sugar, cocoa powder, and vanilla. Stir in 1/2 cup melted butter. Press into bottom of a greased 8x8x2-inch baking pan. Bake for 10 minutes. Cool slightly on a wire rack, about 10 minutes.
In a small saucepan combine corn syrup and 2 tablespoons butter. Stir over medium heat until melted and bubbly. Remove from heat; stir in bananas and rum flavoring. Spoon banana mixture in an even layer over baked crust.
In a small saucepan combine the chocolate pieces, peanut butter-flavored pieces, and shortening. Stir over low heat until melted. Drizzle over the banana mixture. Cover and chill until set. Let stand at room temperature 20 minutes before cutting into bars. Serve the same day. Makes 16 to 20 bars.