Sylvia - I work in the driver team. Our driver does support "automatic scaling" for this use case and it works just fine on DX9 on Win8.1 and it works on DX9/10/11 and OpenGL on earlier operating systems.
As stated in the other thread, it appears that there was some change Microsoft made in Win8.1 that affects DX10/11 - when they are launched in full screen exclusive mode and the user selects a non-native resolution in the game menu, the game requests a mode set and passes in modeset parameters from among the modes that the driver enumerates as available - including what scaling mode to use. Previously we would sometimes report scaling mode "Unspecified" and that came back as "full screen"; For some reason, on DX10/11 on Win8.1 we are seeing this come back as "Center Image". We are working on a fix/workaround for this issue.