In the client-side javascript API, how can I access the submenus of the canvas menu?

[Charlweed]

I can get the options array from app.canvas.getCanvasMenuOptions(). It has two items, with the content "Add Node" and "Add Group". "Add Node" has sub-menus, and its property "has_submenus" is "true". How do I access the sub-menus of "Add-Node" and the sub-menus of each of those?
I expected that the "Add Node" item would have a "submenu" property, but as far as I can tell, it only has two: "content, has_submenu" submenu and submenus are undefined.

Thanks!