[Dovecot] sha-512 ... shadow blended with database

[WJCarpenter]

The cryptic subject is the outcome of my looking into how to do a 
particular thing.  I wonder if anyone else has solved this problem in a 
way that hasn't occurred to me.

I'm using dovecot 1.1.11 on Ubuntu Server 9.10.  I could consider 
upgrading to my own install of a newer dovecot if it made a difference 
to this problem.

I have two populations of dovecot users.  Some users have Unix accounts 
(with logins disabled), and so their password hashes are stored in 
/etc/shadow.  These days, the default configuration for that is salted 
SHA-512.  It's easy for me to change that scheme to something else if I 
want to, but the important fact is that I already have some users with 
passwords in salted SHA-512.  The other population of users is purely 
virtual, and their password hashes are stored in a MySQL database in 
SHA-1 format (unsalted, but moving to salted wouldn't be a big deal).  
The database also has a column identifying the hash scheme, so SHA-1 
isn't some assumption.

I know that I have have multiple passdb in my dovecot config, but I'm 
looking to unify my two user populations and put them all in the MySQL 
database.  As far as I can tell from the wiki, there is no SHA-512 in 
any version of dovecot.  MySQL also doesn't have SHA-512.  So, I don't 
see a way of reworking my password checking to accomodate the salted 
SHA-512 values currently in /etc/shadow.  I'd prefer to not ask the 
SHA-512 users to update their passwords for this administrative reason 
if I can avoid it (but so far, that looks like the only answer).

Any ideas?