That would not be something that the game would handle in any case, that would be an OS/Sound Driver option. I do not know what kind of soundcard you have, but i ran a quick google search and found pretty good guide to do something similar to what you are trying to do. It may or may not be possible with the hardware that you have, so you may want to search around for your specific hardware and drivers.
Here is the guide: http://www.tomshardware.com/forum/55642-6-splitting-audio-headset-speakers
BTW, this guide shows how to have Vent going to the headset, and the other sound going to speakers, so it's not exactly the same but should give you a good idea.