[exim] Routing question

I'm a complete Exim newbie, so excuse this question for being naive.

How can I exclude certain envelope sender domains from using a smarthost?
I'd like all traffic to be sent via the smarthost, except a small list of
domains that will be sent directly to the Internet, bypassing the smarthost.

Here is the existing Exim config:

dc_eximconfig_configtype='smarthost'
dc_other_hostnames=''
dc_local_interfaces='127.0.0.1'
dc_readhost='your.server.name.example.net'
dc_relay_domains=''
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost='smarthost.example.com::25'
CFILEMODE='644'
dc_use_split_config='true'
dc_hide_mailname='false'
dc_mailname_in_oh='true'

Many thanks!
Ken