I don't an answer for the orchid, but the bromeliads don't need soil to grow and will attach them self to pretty much anything. My only caution here is that the cup need to be able to drain so that the brom isn't sitting in water. The Brom will hold its own water and is its placed into wet soil or water collected around the base of the brom, the brom will rot away over time.

I placed on on a piecd of wood and it attached itself to the wood in about a months time.