You are absolutely, the documentation lacks a lot of details on how to achieve certain goals, and we are doing our best to fill the gaps and provide more detailed information on cases of this nature.
The official statement is that the RadDragAndDropManager will be marked as Obsolete as of Q2 2012. And DraggDropManager and the behaviors that are built on it are the official drag drop mechanism. We are currently updating all our examples to use the new mechanism.
As for the issue at hand, the most effective way to achieve the goal you are looking for is to create a ViewModel that is to be used as a Content for the DragVisual which should have a template that reacts to that ViewModel. You can then keep a reference to this object and update it when needed. With the release of Q2 2012, there will be some updates in the Data API in the DragDropManager that will allow you to keep the all the details you need in the Drag payload, not just the dragged data, so it will be easier to implement your scenario.
Hope this helps!
All the best,
the Telerik team
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