This demo (http://demos.telerik.com/aspnet-ajax/editor/examples/treeviewandeditor/defaultcs.aspx
) shows an approach to handle a similar scenario. Based no this logic you can further implement a more complex solution that involves dropping of a more complex data.
Handling content area events can be implemented via the OnClientLoad event as shown in this help article
As for the tool, this is explained and demonstrated in details in this online demo
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