I've known nurseries to just hot glue them to it, craft glue works better though because it doesn't burn the plants, but you can stick a small sewing pin through it into the driftwood (I promise it doesn't hurt the plant that much, I have never heard them scream over it) If you're worried about the toxicity of the craft glue (which I will admit I do not know how it effects the frogs as I don't mount mine that way) you can always try rubber caulk, yet again unsure on toxicity. But whats easier than reading through all of this is this link Care Of Air Plants..Amazing Tillandsia Bromeliads Grow With No Soil