Agree with JieJie. Pretty simple to do on the existing train. The discussion since post #12 was about how to implement this for the upcoming HSR.
Agree with MSPeconomist that it could be done this way. Isn't that what they do on the HK-Guangzhou train? The only problem with doing this with the first stop is that Futian is just minutes away from HK by train, not quite enough time. Unless such train doesn't stop in Futian but then you wonder why they built that station.