SWalker
Warlord
But this methode doesn´t work for scenarios and mods that are using the "El Justo-methode" and cut down the trade-net to gain much higher gamespeed.
With that situation - you can freely overload resources in the colonies, as long as any improvments based on them have the "required resources must be within city radius" flag, because the extra resources don't count as being within the cities radius. However it would be ugly, and confusing (you could have many ghost resources in the same city).
#edit
Additionaly you could use ghost resources to make buildings that can only be built in overseas territories (eg in British Cananda, but not there if the US conqured it). Make a resouce and distribute it to all areas of the map, then create a ghost resource with a matching index but don't place it on the map. Only overseas territories (and unfoutunatly unconnected local cities) would have the ghost resource and be able to build buildings/units requiring it. In a senario like AoI where the major powers are already heavily roaded (so their major cities are already connected when the game starts), and if the the resource was only available to those powers (similar to the colonialism resources visibility), then the only way for major powers to get the ghost resource at home would be to deliberatly cut off access to a city.