[development] Passing options to the front page

I'd like to have some dynamic theme changes to the front page based on items clicked on the front page. What's the best way to do this? I know that ?page= is valid, as is ?q=, but am unsure how to add my own key/value and react to it. If it were another page I'd use a callback, but it being the front page seems to require a different approach. Jeff