Hello Klaus,
AFAIK, you need to define two menus, or submenus. They can have the same commands added to them, but must be two separate items, which you can then add to the respective menus. All menus in FM are linked together in a linked list, which is why the same menu cannot appear in two locations, even if these are never both visible.
I hope this helps. I have been struggling with this and creating two separate menus solved my problems.
Ciao
Jang