How to broadcast to all lists?

Hi All,

I'm looking for some advice on the best way to set up a
"broadcast to all" mechanism with my Ezmlm-Idx lists.  I have
some ideas on various ways I might approach it and I'm hoping the
wisdom of the crowd can help direct my efforts down the most
fruitful path.

Here's the background, current setup, the goal, and assumptions:

Background:
I run an Ezmlm-idx (version 5.x) setup for the local high school.
 The school is using lists for communication to academic,
extra-curricular, and administrative communities.

Current Setup:
There are a variety of lists at the school.  The academic lists
are things like "[email protected]" for Ms. Smith's
algebra class.  The extra-curricular lists are things like
"[email protected]".  The administrative lists are
things like "[email protected]" (ptsa = parent, teacher, student
association).


The Goal:
The principal at the school would like to be able to send out
"broadcast" messages that reach all subscribers.  Conceptually,
the intended list of recipients would be the result of something
like:

{
for list in <LISTDIR>/*
do
  ezmlm-list $list
done
} | sort -fu

Assumptions:
* Subscribers don't get choose NOT to get the principal's messages
* There exists a list people can subscribe to so they can get the
principal's messages even if they are not subscribed to one of
the other lists on the system
* The list of target recipients could be generated by a cron job.
 It is not a requirement to dynamically generate the target list.
 That said, dynamic would be preferred.
* The expected volume of broadcast mail is low.  The principal
will probably send one message a week.
* I don't want subscribers to get duplicate e-mails of any
broadcast messages.

I welcome your thoughts and advice.

Thanks in advance.

David I. Bell