I too have never seen one but it would be very hard to believe that none were made as a bi-product of embers. Im sure someone somewhere has used double hets to make one and poped one out. I think it would look pretty cool if the patty was a high quality with some good color on it.
I saw a few on king snake a few months back, i missed out on them but they really just look like a regular patternless except they have snake/solid eyes and a white nose tip