The owner of this specific site posted a thread about how they achieved their method of doing this. In this case I understand there is some manual work involved from the admin side of things..
http://www.farmads.ie/new/
In the same thread another user has shared their version of the mod which I believe is a more automated approach, but they didn't post their URL. Obviously you can't access that section of the forums so there is no point posting a link to the thread..