I would recommend using the multi-city option. It will build an Itinerary for you if one is available. I have been able to play with it a bit to get the options that I want. Now that they offer the ability to put more city pairs in multi-city it should be easy for you to make it work.

I asked some folks about this during a recent conversation. Admittedly, they are folks in Corporate Communications, not folks in Revenue Management or Route Planning, but at least they were willing to talk.

As of right now if the multi-city doesn't book it there isn't anything they can do. He suggested it might be possible to call and have someone request that it be added as a valid routing but that seems not worth the time on the phone and unlikely to be successful even if it were.