[Exim] Increasing speed of queued deliveries?

Hi all,

Occasionally I have a customer who runs a large corporate mailing list send
it through my Exim servers. Typically the queue is 3x - 4x larger than
normal (approximately 2000+ messages plus). I'd like to nip customer
complaints in the bud before those happen. From the customer-perspective,
they notice late deliveries to their accounts most often. Is there a way I
can tell Exim to deliver local mail as quickly as possible rather than
queue it?

My install is pretty vanilla, so I'm open to any suggestions. I have set
the queue runner to 1/3 of what it was, but IIRC, that does not
discriminate between local and remote deliveries.

Thanks,

-- Steve