I need this modification, too. I have categories with multiple posts, but I want the main menu item to just go to the first post in that category. I also want the other posts to show up as sub menus.
The code that swinggraphics posted works beautifully. However, if you ever release an update, the change is lost, the menu no longer works right, and I have confused or angry customers. If you do have some time to add the code and update on your end, it would be greatly appreciated.