Don't do it! Unless you are doing 100% legitimate online business, and even if that's the case, it's still a bad idea to give google access to your site. If you depend on google to get you your traffic, then I wouldn't let them connect your different sites through wmt. If just one of them looks spammy and G slaps it, then all of your sites could suffer. I even replaced G Analytics with piwik because of this.