Disable (set non-sensitive) an item of the popup menu of a GNOME panel applet

[Eugene Arshinov <earshinov gmail com>]

How can I do that?

I can get a BonoboUIComponent corresponding to the popup menu with 
panel_applet_get_popup_component(), but I do not know how to use the 
returned object.

It would be better if I could get a GtkMenu. I tried to call 
gtk_menu_get_for_attach_widget() passing my PanelApplet object as the 
first argument, but the function returned an empty list.