I must ask: Why are you even considering temperate plants? You are aware that most of these need a dormancy period and lots o light? (An exception would be Saxifraga stolonifera and Mondo grass, two plants that stay evergreen in my NYC community garden. However, both seem to need dormancy to flower.)
As to toxicity--guess what--many tropical plants are toxic to somebody. So what? It is really not relevant to carnivores, and most omnivores and herbivores can handle plants from their region. For example, an East African lizard can bite a euphorbia, an iguana can bite a dieffenbachia.
This is not to suggest that one never needs to be careful. If a bearded dragon ingests an ivy, it will die--you would never get it to the vet in time. But bearded dragons did not co-evolve with ivies!
Still, Rhacodactylus sp. are not folivores (leaf eaters), so you really have nothing to fear here. Why not get something bushy to make em feel (close to) home? A small Ficus, Ardisia or Heptapleurum (Dwarf schefflera) would work, as would a smaller pothos or raphidophora vine.
I assume you have Des Vosjoli's and/or Adam Black's books on Rhacodactylus? Des Vosjoli has a recent piece in Reptiles mag on terrariums for these guys. (Although, one place I am hesitant is to try to keep any of these geckos with frogs; ain't no frogs native to New Caledonia. In fact, it is thought some of these geckos fill the niches).
