I did get to play with a red class with what I presume to be a nak-lok. It appears to be a compression lock, with a hole drilled in the handle to allow the button to be affixed to the lockbar.
That is to say that, while most liner locks are in the front of the knife, to allow your finger to push on it, compression locks are actually near the back of the knife, although the function is basically identical. However, generally, the pressure of the tang is pushed backwards instead of down, and the backwards pressure is further pushed into a bar, wedging the lockbar in between the tang and the bar.
Then, it's a simple matter to attach a button to the lockbar, drill the handle, let the button through. When pressed, the lockbar is pushed down and out of the way of the tang.
Anyway, I believe that's how it works.