I haven't actually tried this, but it should work.
Using 'archivemount' (source from:)
and a 'libarchive' included in many distros (suse, redhat, etc)...
Or a pre-built one from:
You can mount a tar-archive using the fusermount facility in linux.
From there, you should be able to use rsync directly to the final system.
I wrote a simple passthrough batchfile to test rsync's passthrough:
# ussh -- use root@ssh to target system
exec ssh root@"$@"
then, as a test, used rsync to pass dir 'test1' to 'ishtar', calling it /tmp/test2 on the target:
RSYNC_RSH=$PWD/Ussh rsync -uva /tmp/test1/ ishtar:/tmp/test2
It will ask you for the password of the target sys's root logon, or you
could setup the target system to accept a root login via a certificate so no password would be needed.
This would seem to be the most efficient way to do what you want (you might need to modify the rsync options to not copy dir times and things like that), but is this the type of thing you were looking for?