All you have to do to do this is get a program called "Peerblock" its free, then start up wow and in the character select screen start this program up and you will not appear online to your friends but you also wont be able to see them on either, all it does is block the battle.net servers from connecting, oh also I believe you have to have the "block advertisements" option active for this to work. I dont think I am supposed to post links on here but you can just google it its like the first option, has its on name in the website.