Too cold for the free way for sure! It wouldn't take much to mock something up at home with copper or other highly conductive materials. A quick search seems to indicate this is popular as well...

http://organicdailypost.com/make-earthing-mat/

It works, very well for me at least. When the sheet first arrived we just got back from a party where I had been over served. The hangover was terrible however the relief was instant when I wrapped the sheet around my head. The pain would come back instantly when removed so needless to say I wore it as a turban for the next few hours. It also works well for sore or pulled muscles.