"Join" on delimeter aggregate query

Hello everyone,

I've set up PostgreSQL as the authentication / configuration database for my 
mail server (Postfix + Courier-IMAP), and though it works beautifully, I need 
some help on my aliases query.

You see, define aliases in a database table as rows in a column in the form of 
"Source" and "Target".  The problem is that one source address can be 
delivered to multiple targets (e.g. internal mailing list, or a temporary 
forward to another address), but postfix only processes the first record 
returned from an SQL query.

Postfix can deliver to multiple targets, if you separate the targets with 
comas, like so:

Source             Target
joe@bob.org   address1@bob.org,address2@bob.org,....

What I would like to do, is something like the following (I know I'd need to 
group the query, but you get the idea):

Select DISTINCT(Source), JOIN(Target, ',') FROM Aliases

Is there any way this can be done with Postfix?

-- 
Michael A Nachbaur