[villagetinker]

You can carefully dig up the existing outlet and see how the wiring is installed. I am guessing you will need to keep (or replace) the existing box to serve as a junction box. Then install a suitable pipe or metal post to support your new outlet and the conduit between the two boxes. Install the extension wiring and you should be good to go. A word of caution, my understanding to be completely 'legal' this should be done by a licensed electrician.