Multi-Environment S3 Asset Paths If I have three environments; local, dev, and live, and want assets to be setup like this:    

local: stored in a local directory (/public/uploads)
dev: stored on S3 dev bucket
live: stored on S3 live bucket    

What's the best way to set this in a multi-environment config?
Unfortunately, this isn't currently possible.

This feature request is very similar to what you're requesting... however, it would still require that all of your environments use the same type of asset source.