[Mailman-Users] How to Re-write the "To" field.

[Phil Race]

I've got  one-way list, which is getting its data for distribution from 
an upstream system by
mail which bcc's my list. As such the To: field appears as :

"To: undisclosed-recipients: ;"

this is mostly harmless, except for
1) people who reply-all (since the reply-to field I set properly)
2) aesthetic reasons
3) people who subscribe to the list but have filters which
cause the messages they want to be discarded or interpreted as spam.

I have no power to change the upstream system, and what influence
I have would take many months at best to bear fruit.

So I would like to be able to make the To: field be something of
my choosing but it seems I've just reached beyond the limits of
the configurability/scope of mailman.

I have read the various admonitions that mailman is not a CRM system
and trawled the FAQ, but I haven't come up with anything.

Ideas?

-phil.