Shadow Copy - How to configure an external drive as alternative storage volume

Hi All,

I've heard it's been done before and perhaps someone can lead me in the right direction.

As you know in Windows Server 2008 R2, you can go into "Windows File Explorer", you can right click on a hard drive, and select "Configure Shadow Copies".  OR alternately you can run 'vssuirun' from a command box to open up the Shadow Copies window.

We have added an external 5TB drive to the Windows 2008 R2 server via a USB 3.0 PCIe card.  All works and is recognized by windows.  The external drive G: shows up in the "Shadow Copies Window".

We want to set our D2D storage Drive E: to run it's shadow copies on this external Drive G:

When I highlight Drive E: and click on the "Settings" button I can only choose from the pull down, Drive E or C.  Drive G is not available.

When I try another way using a command box and type in the command
    'vssadmin list shadowstorage'  I see the external Drive G listed

When I issue the command  'vssadmin add shadowstorage /for=E: /on=G: /maxsize=95%'
            I get the error “Shadow copying the specified volume is not supported.”

Is there a registry hack or something I need to do to tell Windows Server 2008 to allow this external drive as a viable storage volume for shadow copies?

Thanks in advance.