I had the same problem you have two options you can make some custom battery post connectors or get a new battery with dual post. Autzone sells a great one I don't remeber the model number. But its 800 cold cranking and 1000 cranking. I couldn't post my battery connections as a example for you so the link to my cars site is below. I belive the bolt size you can use is3/8 . I use blank 3/8 thread. And nuts and custom cut it to fit and put a bolt between each connection for spacing and left the orginal post there.
http://www.cardomain.com/ride/2238122/11
http://www.cardomain.com/ride/2238122/11