Probably not as simple as you might think. My wife wanted the same thing. On her LG TV it only had an optical audio output. So what I did was to get an optical audio to stereo converter. Then I added a FM transmitter. She uses headphones that have a AM/FM radio in them. The FM transmitter can be tuned to a blank spot on the FM band. Works great plus she has a radio as well.
Optical to stereo converter:
Hope that helps.