Nope, they can't, either the GDS allows booking it in which case it's already possible or the GDS doesn't allow booking it and then no app can do it. There are

Nope, they can't, either the GDS allows booking it in which case it's already possible or the GDS doesn't allow booking it and then no app can do it. There are plenty services already which allows you to book the craziest itineraries. Like, ITA Matrix Powertools can construct a clickable link into Orbitz from ITA Matrix searches and it doesn't get crazier than that. There's Bookwithmatrix too.