configuring SSMTP

As described here, prior to TMOS 11.5, configuring outbound SMTP was done by editing /etc/ssmtp/ssmtp.conf. In TMOS 11.5 and later it is done through TMSH. However there doesn't appear to be any way to configure ssmtp settings (aside from mailhub) through TMSH:

TMSH accepts:
modify /sys outbound-smtp mailhub mail.mydomain.com:587

TMSH does not accept:
modify /sys outbound-smtp UseTLS Yes
modify /sys outbound-smtp AuthUser username
modify /sys outbound-smtp AuthPass password

Possibly related, this configuration can be created in TMSH but does not appear to have anything to do with SSMTP:

sys smtp-server MAILSERVER {
    authentication-enabled
    encrypted-connection tls
    from-address alert@example.com
    password-encrypted $M$lP$nISJkyprtWrIcPpV93uUfk==
    smtp-server-host-name smtp.example.com
    smtp-server-port submission
    username alert@example.com
}

Could anyone offer advice on configuring SSMTP with 11.5 and later?

thanks!