I have done this. Note that the person who actually drew the the light man is my self. As well as I am in the picture too.
The trick is once the flash fired there should not be much light hitting the sensor where the person is standing.
One thing you can do is choose a darker background for the spot where the person is standing.
The other thing you can try is use a strong flash and don let you subject move even after the flash is fired. The person two does the lightwork needs to move fast in this case.(Even if you subject cant stand still (like a statue) at least their face should not move). Since the flash freezes every thing the little movements of subject will not be clearly visible (Use of wide angle is recommended ).
The other trick is take two pictures and blend those in photoshop.
PS: I dont remember if I used photoshop in the picture or not. Even if I used it is only for color correction. No blending is used at all. I remember using some Instagram filters though.