How can I right justify a menu, such as Help?

Depending on if you use the MenuFactory or not, there are two ways to proceed. With the MenuFactory, use something like the following:

menu_path = gtk_menu_factory_find (factory,  "<MyApp>/Help");
gtk_menu_item_right_justify(menu_path->widget);

If you do not use the MenuFactory, you should simply use:

gtk_menu_item_right_justify(my_menu_item);