Yeah, I can think of a way to do it, you'd just need to render the sequence twice.

#1) Render out whole sequence to tga stills
#2) Render out just the guy at the front in the chair - no need to worry about image quality for this part, we just want the alpha mask of his outline.

Then you could use the alpha channel from #2 to mask the special effect, and prevent it from appearing where the guy in the chair is. And there you have it, your effect appears in front of the guy swinging the punch, but is masked and so doens't cover the guy in the chair, thus appearing to be an effect between the two of them in 3d-space.

I don't use any decent compositing software, but I'm guessin that AE would do it(?)

Simon.