Using glue or epoxy may result in your driftwood "popping up" and taking out your lights
I would be wary of using any sort of glue in my aquarium if for nothing else my fishs' health and especially on a piece of driftwood. I am sure there are many types of "waterproof" glues and maybe some that would be harmless to your "acuatic life" but for me I would stick to patience in soaking, or go with the stainless steel screws mentioned previously.