Add taxonomy as class to adverts

I am looking to add taxonomy terms as classes to adverts (not just the ad groups by all terms) - see http://adaptivethemes.com/give-your-nodes-some-class for an example on other node types. Is it possible to use a pre-processor function (as per the adaptivethemes article) or theming to do this globally for all ad types or does it have to be done for each ad type individually?