I am currently growing Hoya sammannaniana in a straight orchid mix comprised of only three materials Large Fir bark, Large Chunks of Charcoal, and #4 Sponge Rock.  I spray the mix daily to always keep it damp and have a clear saucer under the plant in which I keep just a hint of water in most of the time.  The plants roots have come out of the bottom of the pot and touch the water.  The plant is growing under T-5 fluorescent lighting with high nighttime humidity.  I will report back at a future date on whether this set up continues to work with the plant.