[Exim] deferring mails instead of bouncing when pipe timeout…

Hi,

I am using the following transport for piping through SpamAssassin:

spamcheckbatch:
    driver = pipe
    command = /usr/sbin/exim4 -oMr spam-scanned -bS
    transport_filter = /usr/bin/spamc -p 783
    use_bsmtp
    home_directory = "/etc/spamassassin"
    current_directory = "/etc/spamassassin"
    # must use a privileged user to set $received_protocol on the way
    # back in!
    user = Debian-exim
    group = mail
    return_path_add = false
    log_output = true
    return_fail_output = true
    message_prefix =
    message_suffix =
    temp_errors = *

If the server is overloaded and SpamAssassin takes too much time,
the mails are bounced with the following log message:
"T=spamcheckbatch: pipe delivery process timed out"

Is it possible to defer mails instead of bouncing in case of timeouts?

Thanks,
Marc