If anyone is having problems still using the eChannel leaving China as a result of the boarding pass name check, the magic words seem to be "mingzi tai chang le" (名字太长了). This has worked for me now both at T3 (last month) and T2 (today) where the assistants seem aware of the problem and can manually override the "computer says no" message. You may need to stress also that you are registered (注册了 - zhu ce le) for the eChannel.