I have seen plants that were grown upside down but I have never tried it myself and have never asked those who have precisely how they did it. I may be wrong but I believe it was FDS2Black or FTD2Black or Fdd2Black (or whatever the mod's user-name here is) who posted a picture of a rather nice looking plant that was grown upside down. I may be wrong but I believe it was him. You might want to shoot him a PM or do something to see if you can snag his attention and ask him.
Myself I would have to believe that some sort of weighting or something would be needed to keep plants growing down, something that would be able to overcome their genetic coding that causes roots to grow down and the above soil portion of plants to grow upwards.
That is why people's plants will turn upward and grow upward when upside down, just as the end of a sagging branch or entire sagging plant will turn upward once it has sagged as low as it can go. The genetic coding will always make the above soil portion of plants grow upwards and it will always make root systems grow down.