always_bcc only after reinjection from amavis

[btb]

hi-

i have a server which relays mail to our content filter server
[amavis/spamassassin/etc], via:

content_filter=lmtp-filter:[mfa.${mydomain}]:lmtp-filter-internal

and returns, via:

# reinjection from content filter
smtp-reinject-internal
    inet  n       -       -       -       -       smtpd
        -o syslog_name=postfix/smtp-reinject-internal
        -o smtpd_banner=${smtpd_reinjection_banner}
        -o content_filter=
        -o local_recipient_maps=
        -o relay_recipient_maps=
        -o smtpd_client_restrictions=
        -o smtpd_helo_restrictions=
        -o smtpd_sender_restrictions=
        -o smtpd_recipient_restrictions=smtpd_reinjection_restrictions
        -o smtpd_relay_restrictions=
        -o smtpd_error_sleep_time=0
        -o smtpd_soft_error_limit=1001
        -o smtpd_hard_error_limit=1000
        -o
receive_override_options=no_unknown_recipient_checks,no_header_body_checks,no_milters
        -o local_header_rewrite_clients=

i'd like to use always_bcc, to copy all messages to an archival system,
but only after the messages return from the content filter server.

how can i do this?

thanks!