Hi everyone! I just wanted to reply to the question. I have been putting my orchids with little or no medium in a regular pot with holes at the bottom and the sides. I just put enough lava rock so that the plant does not fall over. If it stands up with nothing in the pot, then I just leave it the way it is - with no medium.
There is of course, no risk of root rot although they do dry out quickly. You might have to water everyday or every other day is fine. I just water with a misty kind of hose and let the water drain out of the bottom of the pot.
I just came back from the PHilippines and all lot of people there just tie their orchid roots to a tree branch, cover it with a section of coconut shell and that's it! The coconut shell is optional.
My cousin just sticks hers in ivy and she doesn't even water any of her orchids!! They do well. Temperature in the PHilippines ranges from around 85F-95F everyday. So orchids are used to hot weather. I think it is because the Philippines is very humid so that even if it doesn't rain, the roots just get water from the air.
So the answer to your question, I think is, it is ok to do it without medium, just as long as there is good drainage and air in the pot.
Good luck!!