My users needed this functionality too. In my case, a subset of sites need the same documents, the documentation is edited about every other month. Having to go through and update each site containing the documentation would be horrendous (approximately 300 sites).
The repository supports this but its not exposed to the Share UI. You can write a fairly simple script to do this. Here's an example.
<javascript>
//this is the node where you want the document displayed
var targetNode = document;
//this is the node you want to display in multiple places.
var sourceNode = utils.getNodeFromString("workspace://SpacesStore/f5ae0fe7-1f12-4547-a832-dacf3fc915d9");
if(sourceNode){
targetNode.addNode(sourceNodes);
targetNode.save();
}
</javascript>
Edit the source node's nodeRef (or use another search method), then in the Explorer interface, execute it against the folder where you want to see the new node.
There it is. All edits to the source node will be reflected in the new location.
Just note that the site members of the target site are going to need at least read privileges to the content where it originally exist.
