Simple enough, after trial and error with each patch I have discovered that it is really easy. Only patch your main folder of WoW. Then copy all folders/files except those that are simlinked into the other installs of WoW. Once this is done you can launch all copies of WoW as usual and only have to patch one copy of WoW. Anytime you launch one of your simlinked installs you are going to have troubles without doing it this way or a reinstall. Just be sure and backup your Interface and WTF folders on a regular basis and always before a patch.