The APEX Plugin wasn't created with an option to have only a top level button and no children, it assumes all top level buttons will have children.
You could edit the plugin and modify the code to add the url to the top level buttons.
Or you could try the Enkitec Navbar plugin which might give you what you want and allows top-level links.
Thanks, I will attempt to modify plugin code. Have created demo applications using Enkitec Navbar plugin along with Steve Wesley's solution and am trying to determine which solution to go with.
I like the Enkitec solution but not the flickering of the list entries prior to the rendering of the menu but have yet to see that solution with the CSS stored on the server versus embedded within the application.