All that is needed is to write a function that registers to copy action, grabs the copied selection text, adds on a copyright notice and then send those two to the clipboard. Just add this code between your page’s head tag (works also inside body section).
This seems to work well on Firefox and according to original article also with most other browsers. Sorry IE people, this one won’t work for you.
This is already in use in ePanorama.net documents section. Go to any document and try cut+paste from any document there.