[Exim] Advertising different AUTH over STARTTLS sessions?

Now that I've converted my RADIUS servers to support CHAP authentication I
have a cleartext password available for my users so I thought I'd enable
CRAM-MD5 AUTH on the mail servers. However, what I'd like to do is allow
CRAM-MD5 over a cleartext SMTP session and PLAIN, LOGIN, and CRAM-MD5 over a
STARTTLS session in Exim 3.34.

I thought I remembered some discussion of this sometime back but I can't
seem to find it in the archives or FAQ. I'm also not seeing any appropriate
auth_ or tls_ commands which suggests it isn't possible. Is there any way to
do this in 3.34? If not, is it possible in 4? And in either case what would
I need to do to support this?

Thanks,

Tabor

--
--------------------------------------------------------------------
Tabor J. Wells                                     twells@???
Fsck It!                 Just another victim of the ambient morality