Preheat oven to 325 degrees. Coat a 10-inch tube pan or 12-cup Bundt pan with canola cooking spray. Sprinkle the nuts over the bottom of the pan. In a large mixing bowl, combine the remaining cake ingredients (cake mix, egg, egg substitute, pineapple juice, sour cream, dark rum) and beat on medium speed until well blended. Pour the batter over the nuts in prepared pan. Bake in the center of oven for about 50-60 minutes or until cake tester inserted in center comes out clean. Let the cake cool completely, and then invert it onto a serving plate. To make the glaze, melt the butter in a small, nonstick saucepan. Away from the heat, stir in 1/2 cup rum, 1/3 cup sugar, and 1/3 cup Splenda. After you've stirred the mixture, put back on the stove over medium heat and bring to a gentle boil. Continue to gently boil, stirring constantly, for about 4 minutes. Let cool for about 5 minutes. Prick the top of the cake all over with a skewer or large barbecue fork. Slowly spoon or pour the glaze evenly over the top. You can spoon or brush some of the glaze that drips off onto the sides of the cake