How can I control Panasonic plasma TV volume through headphones that use audio out sockets on rear of set?

These sockets are not meant to be used for headphones, but as I am hard of hearing they could be very useful. I do use them for my headphones, but sometimes the inline volume control cannot reduce the volume enough to avoid my ears getting blasted during very loud scenes. My previous TV (Hitachi) had a phono socket that had a phone volume control that was adjustable seperate from the speaker output & that worked very well for me