Menu parent and slide out sub-menus

If you look at the magazine demo at http://demo.gavick.com/joomla25/magazine/ the menu item 'categories' has the slide out sub-menu with tablets, tvs etc

This only works when, like in this example, the menu item (categories) has a parent item (home).

So I can get it to work, but then my URL for any of those links looks like /parent_item/menu_item/page and I want it to be just /menu_item/page

How can I do that? Is doing a mod_rewrite the only way or is there a way I can achieve that within the template.

Hi

This is the way mega menu works, so yes an overrie on .htaccess, but I would advice to use some of 3rd party sef links components, where urls ca be changed cannonicaly.