Tell the wallet owner to create another new wallet.dat (never been used), encrypt it with the exact same passphrase used before, and then import those addresses.
Thanks for the suggestion,I'm asking because I don't know, how does he import those addresses?
I'm trying to remember what I did. My case was a little different as I was recovering from over writting an encrypted wallet with an old, unencrypted, backup, and I might be confusing things. Perhaps it was encrypting a new install with the exact same passphrase, exporting the private key, and then importing that private key into the outdated backup that saved my coins.