How to Open a Rooted View of a Junction Point Through the Registry
You can use the registry to specify that browsing into a junction point will open a rooted view rather than the default view of the contents of the associated extension.
To specify that browsing into a junction point should open a rooted view, add Open\Command and Explore\Command subkeys to your extension's CLSID subkey, with their default values assigned to the command lines shown here:
HKEY_CLASSES_ROOT CLSID {Extension CLSID} Shell Open Command (Default) = %SYSTEMROOT%\explorer.exe/e,/root,"%1" Explore Command (Default) = %SYSTEMROOT%\explorer.exe/e,/root,"%1"
Once you've added those values, an instance of Explorer.exe is launched to display the contents of the extension as a rooted view when the user selects the junction point.
Specifying a Namespace Extension's Location
How to Open a Rooted View of a Junction Point Through a Shortcut File