I don't think that this could be achieved without basically recoding how the menu works. The reason is that the menu makes use of css states for the affects you are seeing, so for example the second level nav shows when the hover state is in effect for the level one item. This is not something that you would be easily able to update. The process would involve using some custom client side js code to dynamically change out the styles applied based on events like onClick and onMouseOver. For the css you could reuse the existing styles and classes that have already been created, you would just need to use the js to make the change rather than let the css handle it.