Intrigued by this idea, I went t'net to investigate. There is a youtube video from Pana about recording to HDD. However, they seem to want you to have a dedicated HDD, not just a bit on the side of an HDD used for, say, back up.
Some panas are scart-less. Have you tried a scart to a recorder?
Go to Utoob and look for
"How To Use DLNA And External HDD On Your Viera TV"