Hi,
change them all together via db, it's nothing else then a remote image url.
If you keep the directory structure i think it must be possible to change them
in a row via sql command from media_file to remote_media_file while adding
the front of the absolute path.
Maybe you have to do something else before so if you try have db backup
and only rename the source data folder for testing (before you delete it).
I don't know the proper sql command (i hate sql) maybe one of the elite guys
can give u a hint.
Greetz X23