disable sieve replication with dsync

Hi,

I think I got dsync working for mail, but I'm getting these errors:

Error: sieve: file storage: mkdir_parents_chgrp(/usr/local/etc/mail/mandelberg.org/david/sieve/tmp) failed: Read-only file system

I'm managing sieve files externally, and I don't want any part of dovecot writing to them. Is there any way to configure dsync to not replicate them? I looked at doveadm-sync(1) to see about adding a flag to replication_dsync_parameters, but the closest thing I see is -x for excluding mailboxes. Or maybe -o? Is there a way to specify a nested setting to -o, so I could do something like plugin { sieve = } for dsync?