I think you misunderstood some here. I said upload as user was used on a one by one basis.
The upload as photos option is limited to specifying one username. Therefore it is not compatible with doing a bulk upload since these photos your importing are from all users.
You only have two options bulkupload the attachments folder in
vb which means you would own all photos and then go through and edit them one by one and reassign them to the proper user or download your attachments folder upload them one at a time in photopost and specify the proper username.