How do I configure the Apple TV so that I dont have to use a second HDMI cable
You don't. AppleTV has no control over how your TV or cable box work. So there is nothing you can do it to change how those devices work. If the cable box has an HDMI input ( NOT an output ) you can trying connecting it there and selecting that input from the cable box. Otherwise you just plug it in to an HDMI port of the TV. Which is more likely to work better any way.