What about doing something along the lines of:

rm -rf $LJHOME
git clone https://github.com/dreamwidth/dw-free.git $LJHOME
cd $LJHOME
git remote rename origin dreamwidth
git remote add origin https://github.com/[username]/dw-free.git

And then prompt the user whether or not to pull from their origin? If they try it and pull, and the hack is still broken, they can run it again and not pull, and telling it not to pull will also tell them how to go about recreating their forks?