Here's some reading for ya
http://en.wikipedia.org/wiki/Ozone_cracking
It doesn't provide anything in terms of any aftermarket treatments to prevent it but I would think that you could check the labels of tire products at your local car shop to see if anything is listed for protection against ozone.
BTW, click on the external links at the bottom for more reading (something from General tire on the subject).
Here's one product that specifically mentions prevention of cracking by adding a anti-ozone polymer agent. I'm not endorsing this product, just giving a lead on searching for a product that will meet your requirements.
http://www.meguiars.com/estore/produ...ectionID=18101