That card does not need an interconnect cable. It will use the system bus to initialize crossfire. The DVi dongle was the very first way to connect 2 ATI cards in crossfire back in the x1800/x1900 days.
May I add, you mentioned the (2) cards you want to get. I am assuming you do not currently have them. Unless you are running 4 displays, I would suggest getting the 5770 for the same price as (2) 4670 cards. http://www.newegg.com/Product/Product.aspx?Item=N82E16814161310&cm_re=5770-_-14-161-310-_-Product
OR even a 5750 for a lower price if you do not need the performance. http://www.newegg.com/Product/Product.aspx?Item=N82E16814150448&cm_re=5750-_-14-150-448-_-Product