Merging a taxonomy menu with another menu into same menu, to be used as a nicemenus block

I'm trying to merge a taxonomy menu with other static menu elements.

I want to take the output of the taxonomy menu and merge it with other menu items, but still keep the functionality of the taxonomy menu (re-build taxonomy menu when new terms are added, etc...).

I could create the taxonomy menu and then manually add the normal menu items to it, but the menu, when it is re-built, would over-ride my new menu items, replacing them with taxonomy-only menu items.

Is there a way to have a "top level" menu with the items within it referencing other menus, creating a nested menu structure, with each sub-menu being it's own independent menu, but allowing me to place the complete, top-level menu in one block (specifically for nicemenus)? Something like this:

Menu 1: (nice menu)
- link 1 (normal menu item)
- menu 2 (menu item is actually a reference to another menu)
- menu 3 (menu item is a reference to taxonomy menu)

Keywords for search: merge menus, taxonomy menu, nicemenus, hierarchical menus, nested menus.

I will keep researching this and post results when I find a solution.