[Exim] Using filters to streamline "mail merged" mailshots

Hi folks,

I'm setting up a mass mailing system designed to send "personalized" or
"mail merged" messages to a large list of subscribers.

The personalization requires substitution of real name and other details
for macros in the submitted message text (including the cosmetic From:
field).

If I inject a message per recipient, the hit on the disks is going to be
enormous.

Today, it occured to me that I might be able to use lookups in a filter
to do the "peronalizing" after routing but before smtp transport time.

I've thought of a couple of ways to do this, but they all involve
individual copies of the message hitting the queue. Can this be
avoided?

I'm not looking for a HOWTO, I'd just like to know whether this is
feasible, so as not to waste time trying something that can't be done.

Ciao,
Sheldon.