Unless the game has a menu feature for that, you won't be able to achieve it.
Even so, stereo headphones have only 1 driver, meaning its point-source, and can only vary in sound amplitude. Any "emulated surround" speakers/headphones will have multiple drivers.
His Sound Card MUST have capability to "Emulate Surround" too.
You MUST fit on all the 3 points here:
1.The game must have a menu feature for that(Emulated Surround OR 3D Sound OR Surround, any of the these should work for what you want)
2.Your Headphone must have multiple drivers(some headphones have that)
3.Your Sound Card must have capability to Emulate Surround.
Without ANY of the 3, your attempt will just be in vain.
The "X-Fi CMSS-3D" is the part of it that does this. There are probably other audio devices by Creative that have this too. But the Xmod is what I have tried.
It really does give you surround sound, and not just reverb effects. It creeped me out the first time I ran a 5.1 sound test with my headphones on. It was like the sound came from behind me.
When you plug in the Xmod, it tells the computer it has 6 speakers connected (like a traditional surround sound setup). Applications that support surround sound can send their surround audio to the Xmod, and it somehow transforms that into a 3D sound over 2 speakers.