Allow contributors to moderate comments comments on posts they write

I run a multi-author wordpress site where we have a large number of contributors that can write articles, which are published after they are reviewed by an editor. (This is all standard wordpress behaviour).

What I would like to do is give the contributors the ability to moderate comments on the posts which they write, but not on posts written by other people. I haven't found a way of doing this, either with a code snippet or plugin and am hoping that someone here knows how to make this work.

Thanks

EDIT: I forgot to mention that I am running multisite.

Thanks again.