How to set paths for menu items in hierarchy to make it work with Superfish
Weirdly enough I've just stumbled across the Special menu items module, which is:

a Drupal module that provides placeholder and separator menu items.
A placeholder is a menu item which is not a link. It is useful with dynamic drop down menus where we want to have a parent menu item which is not linking to a page but just acting as a parent grouping some menu items below it.

I'm pretty sure that's just what you're looking for, and it has a stable release for Drupal 7 :)