For default Microsoft HD Audio driver, on the playback device list, double click Headphones, this will open the Headphones Properties
window, select Enhancement
tab, then enable Headphone Virtualization
, Studio
option seems to work best for me.
With above settings, you'll hear the original left and right channel on left headphone -- or right headphone, these two are the same now. Tested with this youtube video, but not sure about the specified game though.