You wouldn't do it in the cart object. You would combine it on the display page. If you attach the cart display page then I can show you what lines to update.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.