[exim] More secure authentication with dyndns.com's mailhop …

The mailhop outbound knowledge base for Exim [1] says to use this
authenticator:

        login:
            driver = plaintext
            public_name = LOGIN
            client_send = ": username : password"

I mentioned previously [2] that I'm not really happy about having the
unencrypted password on my hard drive (since the mail authentication
password is the same as the account password). Peter Bowyer said
there are other ("several dozen") ways to do it, but I haven't been
able to figure out what to do.

I would like exim to be able to authenticate to outbound.mailhop.org
without storing the unencrypted password on disk. Is this possible?
If so, I'd appreciate some advice.

Thanks,
Adam


[1]
http://www.dyndns.com/support/kb/archives/mail_servers_and_mailhop_outbound.html#exim

[2]
http://www.exim.org/mail-archives/exim-users/Week-of-Mon-20060327/msg00189.html