Sadly, no, as any such trilateral agreements are usually negotiated on a case-by-case basis by the involved countries. There is no way for us to track all of them, so we rather keep it simple.
I am not 100% sure I understand what you mean, but I guess you’re trying to say that you’d like to sell only A-C but not A-B and B-C individually? If so, than that is something that would be supported in the future by fares and, depending on the structure of the network, some additional fare/routing rules.