If you want to make the FileExplorer access files and/or folders outside your application's root, you will need to implement a custom FileBrowserContentProvider.
The FileBrowserContentProvider abstract class allows for different file sources to be used in the RadFileExplorer control, such as file system, database system, CMS-specific resource system or even online storage systems such as Amazon S3. You can find various custom content providers in the KnowledgeBase
sections of our site.
I believe the content provider from the following KB article will be suitable for this specific scenario:
Use RadFileExplorer with physical and shared folder's paths
In addition, you can find more detailed information on how the content provider works in the following help article:
Using custom FileBrowserContentProvider
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed