Depends upon the species. Those with a clear delineation between the living tissue and the central bony axis or gorgonian are best done as follows. The tissue is first scraped away from the section that is going to be under the epoxy. The gorgonin section is then inserted into a hole in a rock and then putty epoxy is used to secure it in place. The live tissue should not be imbedded into the epoxy. The live tissue will quickly grow down onto the epoxy.
I have a form of thick branching gorgonian that does not have a clear delineation I mentioned above. For this one I just cut a chunk of it and wire it to a piece of rock with some fishing line. Must not be too tight. The tissue will grow down, encrust, then grow up to form new branches.
The non-photosynthetic ones can be propagated the same way, but they are REALLY hard to keep because they have to be fine fine particulate food, very often.