[Duplicity-talk] three way backup?

[Andreas Schuldei]

right now duplicity operates in a two way manner: 

1. source   2. target

for backups to DVD+-RWs i use growisofs and would like to do
full backups the normal way: 

duplicity /some/where/on/filesystem file///some-tmp-dir

and from that tmp-dir i then write all files to DVD+RW with
isofs.

for incremental backups i would prefer not to have to copy the
backups back into file///some-tmp-dir to be able to operate on
them, but instead just point duplicity at the DVD+RW and tell it
to write the incremental backup to file///some-other-tmp-dir,
from where i then would add them to the isofs on the DVD.

Is this possible? how can i do this?