Not sure if it's stillpossible since after going there a few times back when BC first came out I haven;t had the interest BUT it certainly WAS possible to get there. There was an altered patch.mpq file floating around that when dropped in your wow folder would alter the course of the zeppelin from org-booty bay and bring you to GM island. This was NOT the instanced gm island but more of a placeholder it had the house the lake and the misc things there but not the portals and everything the old gm island that IS now isntanced had.
Basically you had to get on the zep log out reload with the mpq in your folder and stay on the zep for seriously like 30 minutes before it would get there.
Here is a pictures to step by step instructions on how to do it.
Here is the completed file http://www.freerichie.org/gmisland/speech2.mpq
The above file was for teh boat from darkshore to darnassus because I couldn;t find where I saved my horde one.
Hope this helps osme of the naysayers. Like I said I don't know if it's still possible but this IS how it used ot be done