I have made the files to do this, however I can't find a place to "zone in to the instance" with accurately.
for example the map loc you need to be at when switching instance is:
Black Morass (7142, -2005, 23)
That 7142 co-ord is wayyy off teh map both for azeroth and kalimdor, could prolly get there via a zepellin maybe but don't wanna get banned for it
I have successfully re-created OLD hillsbrad and zoned into it though, both the hillsbrad and BM files are in the same .MPQ file which I will upload somewhere for peeps to download from.