vol copy can copy snapshots as well.  From 7.2.6.1 vol man page, 
vol copy start [ -S | -s snapshot ] source destination
              Copies all data, including snapshots, from one vol-
              ume to another.  If the -S flag is used,  the  com-
              mand  copies  all snapshots in the source volume to
              the destination volume.  To  specify  a  particular
              snapshot  to  copy, use the -s flag followed by the
              name of the snapshot.
 Though I'm not sure this would be any faster than a snapmirror. 
Andre, I'd be interested to hear what your outcome of this eventually is.