If you want to use symbolic links it's actually quite easy. Have two separate WOW installs, then in your 2nd install delete the DATA folder. Now create a symbolic link to the original WOW's DATA folder and you're good to go. Then you only have to patch your main wow and the other one should be already up to date when you launch it.

JUST MAKE SURE you never delete the DATA folder in the 2nd wow thinking you're just going to delete the link, that will actually delete the real DATA folder as well...if you want/need to break the link you have to use your software tool to break the link first, after which you'll be left with an empty DATA folder in the 2nd WOW which you can safely delete.