To add the CD key, that worked for me:

In the install folder (Right click > Manage > Browse Local Files) there's a file called installscript.vdf

Edit it and add the following to the registry section:

    "HKEY_CURRENT_USER\\SOFTWARE\\Futuremark\\3DMark"
    {
        "string"
        {
            "KeyCode"		"<YOUR KEY HERE>"
        }
    }