You can book W fares on AF and VS through Delta. Just set the fare class to W or above. Actually, I found that setting the advanced search to B or higher saved a little bit ($100-200) on the domestic connections, which then booked into Y (and upgraded into F at the time of booking) instead of A. I am generalizing from searches and a booking last fall.

Of course, none of the above is helpful if what you really want is to upgrade from W fares into BE. But if you're willing to settle for Premium Economy, I think it's a pretty good deal, given the additional MQM and RDM.