[Exim] Handle only some addresses in a domain?

Hi,

I have a situation where I want EXIM to handle only some of the
addresses in a domain. Our US office is the primary MX for this domain
and it is company policy to address all emails using this domain rather
than a sub-domain.
I want my local copy of EXIM to catch any outgoing messages that would
otherwise be passed to the US server, converted to a sub-domain style
address and then passed back to my local server for local delivery.
Is this possible?

Joe