Dynamic MenuItem Support

I am trying to add items dynamically when the user clicks on a menu. I have tried to clear items and then add them in the command handler, but that does not work, as there is no immediate mode on the menu item. (I assume this is by design to keep the menu client-side)

I would like to either:

  1. Simply add a combobox or list to a menubar/menuItem.
  2. Add a handler to the item to fire just before the menu opens.

Does anyone have a suggestion for a workaround besides not using a menu for dynamic content?