Hi Andy,
one method would be to copy the entire backup database to another drive.
This is not convenient and may also consume some space for unnecessary backups, since you cannot distinguish between different computers.
Otherwise you also could register at Connect, as outlined
here (only the lines with the links for registering are interesting in this case for you) and file a suggestion for a feature, which allows to export parts of the client backups.
Best greetings from Germany
Olaf