Hi Dennis,
If the Column Headers are normal menu items, ShiftNav will process them that way (as opposed to advanced UberMenu items). You can disable individual items in the menu in ShiftNav only, but that will disable their children as well which I assume you don’t want to do.
Apart from writing a bunch of custom PHP to rearrange the menu programmatically, the simplest solution is likely to just create a separate menu and assign that to ShiftNav. If you want you can use the Menu Duplicator to quickly copy the menu.
Hope that helps 🙂