Well, I remember that some time ago I found on internet some kind of book or alike apparently written by martino, explaining the system.
Other than some mystical I-ching related stuff to justify his choice (which I see totally unnecesary, I mean, you can play whatever you want don't you?), I think the key here is to know your substitutins. I pretty much suck at this right now, but it comes with time. Just knowing that you can play Bm7b5 or Bº7 over G7 if you want a G9 or a G7b9...that's the beggining, and where I am.
Then it's mostly a matter of SOUND basically, and it doesn't relate too much to traditional harmony. I'm not there yet, because I can't hear the chord sound in advance, but my teacher has shown me how he does it and its mostly a thing of sound (clashing a 7 with b7, which in theory is wrong, can be a beautiful sound depending on the context, that kind of things).