[Exim] multiple-recipient queueing

I have the following UUCP setup which works well:

# UUCP Transport to send mail to my upstream ISP:
uucp:
driver = pipe
user = nobody
command = "uux -r - agate!rmail $pipe_addresses"
return_fail_output = true

# UUCP Router
uucphost:
transport = uucp
driver = domainlist
route_list = * bydns

But my objection to this setup is that I can't figure out how to tell
Exim not to create multiple messages in the queue when there are several
recipients.

I want the functionality that you get when you use a smart-host: A
single message goes to the ISP, and only there does it get replicated.
Trouble is, I can't work out how to get smart-host functionality with
UUCP (well actually uux in this case). Is it possible ?

Many thanks,
Thomas