I'm using WPMS and am trying to combat attempts of it being used as a link farm. I would like to make all of the sites have rel=nofollow by default, and then allow me to disable this on a case-by-case basis.
I searched for a plugin to do this, but didn't find it. Any ideas how to do it? I know I could edit themes, but I try to keep them stock so they can be updated easily, plus there's hundreds of them, and I don't want to have one set of themes for trusted users and one for non-trusted users.