I have CarrierWave working fine through the typical ORM setup and upload via form. I would like to figure out how to use CarrierWave outside of the form submission context.
Actually you can do this using the built in remote_{attribute}_url property if you are using the active record/model helpers (see the CarrierWave railscast for the details). However, I dug around in the source code a bit to see how this actually works and it appears that even if you are not you should be able to use the following:
uploader = ImageUploader.new
uploader.download! some_remote_url
uploader.store!
Give it a try.