They actually attach to the rock/wood. Mine send roots down to the substrate. If the anubias is up high enough in the tank, the roots add a very nice natural feel to the tank. Click my sig, I have some close ups of mine on driftwood.
If you have a walmart near you, in the arts and crafts section (decorative rock) they have little mesh bags of "tiger rock" which I have in my 29g, I think they would look fantastic with your substrate. Give them a short fall into the tank and aim for a pile lol. You have a great concept, with a little work and tweaking. Your tank could be stunning. I think some stargrass planted around the driftwood, trimmed to be short up front and taller behind it would make the wood pop.