There are certain countries and airlines where one cannot just book and pay as one would like or is accustomed to.
Domestic China flights is one example, as you are discovering.
Another example that I often run into is booking flights on Batik Air in Indonesia - using a Canadian credit card , whether Amex, Visa, or MC always
errors out. My solution: use a travel agent - usually a local Indonesian one ( Nusa Travel).
The convenience that Nusa and Ctrip offer me is the ability to book the flights and fares that I want when I cannot do it one the airlines web sites.
Just accept that what you want to do cannot be done, and move on to another solution.