carrierwave - Overriding uploader version with an image from a remote url

Question

How can we override version method to extract an image from a URL instead of processing.

Basically, How can we do something like this:

version :normal do
    if model.is_facebook_image?
        #help needed
        #get image from facebook graph api: http://graph.facebook.com/model.fb_id/picture?type=normal
    else
     process :scale => [100, 133]
    end
end