Add a button to the object add pannel's grease pencil menu

Archive Python API
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How can I can i add a new button to the Shift + A object add panel under the grease pencil menu? I would like to customize it. For the mesh pannel it is easy with defining a operator subclass and:

def menu_func(self, context):
    self.layout.operator("my.operator")

bpy.types.VIEW3D_MT_mesh_add.prepend(menu_func)

But there isn’t a VIEW3D_MT_gpencil_add.

Also how could I remove an existing button or the entire Grease Pencil menu? (In case there is no way i would recreate this submenu then. I guess is the only way to customize it)