PyMEL: Adding dropdown menuItems to an existing shelfButton?

Coding
1 
myButton = pm.shelfButton(
    annotation=myAnnotation,
    command=myCommand,
    image=myImage,
)

pm.shelfButton(myButton, edit=True,
    menuItem=(myAnnotation2, myCommand2)
)

Problem here is that the menuItem flag is not set for the item.
Problem two is that the menuItem flag can occur multiple times and that I want multiple items

Is it even possible to add new flags to existing UI controls in this way?
Even if I have say 4x menuItem -flags coded in when I create the button, how can I access them individually once the button has been created?

The documentation is super-helpful on this topic, with no descriptions of the flags (other than data type) and no example code. I mean, what the heck does the menuItemPython -flag even do?

2

From… Command ref…
This flag is used to specify that a menu item is in Python. The integer value is the index of the menuItem which is modified by this flag. This is 0 based, so it corresponds to the (index+1)th occurrence of the /-mi/-menuItem flag.