gmkah1 :
The cable is wired directly through the TV. Any other ideas besides buying another new set? This TV is new and not returnable.
How handy are you with a soldering iron? You could take the TV apart, find the analog audio wires going to the speakers, and rig up a mechanical switch on them allowing you to choose between using the speakers or a headphone jack which you'd also have to install.
The only other option is to buy a TV tuner box instead of using the built-in one on the TV. If you have cable TV, then this is just a regular set-top box the cable company provides you with (yes you can buy those, you don't have to rent them from your cable company).
If the TV is getting over the air (OTA) signals, this is trickier as Hollywood and the TV studios have mostly succeeded in eliminating aftermarket digital OTA tuners from the market. You're probably better off one of the digital converter boxes for allowing you to view digital OTA broadcasts on an older analog TV. The picture quality would be degraded to 480i, but you will get a separate audio out. (If he only likes to watch one channel, you can just put this beside his bed, tune it to that one channel, and have him use it just for the audio. Have him mute the TV when he uses it.)