That is brilliant, espesially the "not limited to the Bible" part. So, how do you choose which parts are to be taken metaphorically and which are not? Which parts of the bible do you believe in?
Certainly the obvious metaphors: visions, dreams, prophecies, poetry, songs, allegorical stories, and parables, have to be taken as such.
As for the rest, it's a discerning process: If a particular "historical" scripture contradicts with most other credible historical evidence, then look at that verse from the writer's perspective, and see what a biased history teaches us about our faith. If a particular "scientific" scripture contradicts with most other credible scientific evidence, then look at that verse through the eye of the writer to see what was observed to make the writer come to this conclusion while attempting to put God's Words into human words.
Basically, we just look for God's Truth in words tainted by human ignorance, pride, and bias.