Hi,
I'm attempting the same thing. I followed the directions for smtp-user/pass, so I thought, but I get an error.
2016-10-02 10:06:18 Exim configuration error in line 587 of /etc/exim.conf:
router auth_relay: cannot find router driver "smtp"
Then I tried the patch -p0 method with a fresh exim.conf. After editing the exim.conf file for authentication, I get this error:
2016-10-02 10:35:03 Exim configuration error in line 497 of /etc/exim.conf:
error in ACL: unknown ACL verb "driver" in "driver = plaintext"
It looks to me that it just hates driver declarations.