[exim] Passing variables into exim?

Hi,

Is there any way to pass variables into exim externally? I want to do
something like:

spamcheck:
driver = pipe
command = /opt/exim/bin/exim --set-acl_c0=$acl_m0 -oMr spam-scanned -bS -os10m
transport_filter = /usr/bin/spamc -u $local_part@$domain
use_bsmtp = true
batch_max = 1

i.e. tell the target exim process the contents of a variable calculated
during initial ACL processing.

Alternatively, is there a way to access environment variables from within
exim variable expansions?

thanks,

Matthew.