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.