Hi John,
While I have not done this, I think it should work fine but do not know for sure. Hopefully others will be able to confirm the information or not.
Install the Vail Beta Refresh on the system. Do not add the backup drive to the system as it will then be formatted. Using everyones favourite unsupported remote desktop connection, open the shared folders on the server desktop along with an explorer window.
You should see your internal backup drive showing as a seperate drive. Simply use normal window copy, paste, moves, etc to copy the data from the backup drive to the newly created shares. Once you have copied the data across the backup drive can be added back
in as the backup drive.
With the change to DE in the refresh install, I am not sure whether the old shares show up as non default storage or not and whether if they do the data would be readable or not.
Dave