Your plan is promising, but Aperture has a built-in feature to do just that. So Aperture could do that for you, if you mount the backup volume. You need to do three things:
- Create a smart album, that contains all files with missing original files.
- Use Aperture's built-in command "Locate referenced Files" to point Aperture to the location on the server and to connect the versions again to the originals.
- Use "Relocate orininal(s)" to move them all to the to "Pictures" folder again.
To find the images that reference the backup volume, define a new smart album containing the missing originals:
File > New > Smart album
In the smart settings HUD press "Add" to add a rule "File status is" and set it to missing.
To reconnect these images, select all of them at once and from the main menu bar choose
File > Locate referenced file.
Now you will see the reconnect panel. In the upper part you select a file that needs reconnecting, in the lower part you can point Aperture to the location of the file on your backup volume. If the files match, the reconnect buttons become active and you can press "Reconnect all".
Hopefully this will reconnect all at once.
After reconnecting use "File > Relocate Originals" to move them back to your Pictures folder.