I'm not sure if it works or not with the GOG version, but a review linked to here: http://www.3drealms.com/duke1/index.html -> scroll down to Downloads -> duke1ed.zip

Let others know if it works (I can't test it), if there are special things needed to get it working, etc.

It seems to work just fine with gog, just know that you have to save your levels over the game's original episodes to play them, so be sure to back up the old levels if you want to play them again without re-installing the game, and read the .doc file included.