I have video model with the following definition:
class Video require \'carrierwave/orm/activerecord\' mount_uploader :attachment, VideoUploader mount_
This worked for me, with CarrierWave 0.5.8
model.update_attributes(:remote_uploader_url => "http://path/to/image.jpg")
Of course, you need to set remote_uploader_url to be attr_accessible for this.
remote_uploader_url
attr_accessible