[Exim] 'forwarding' mail through a relay.

I hope the subject line is not too confusing, I am not too sure how to
describe the problem, and sorry of this is obvious, I am new to exim
(have always used postfix before).

We have a redhat/exim 4.24 mail and web server (server A) and we are
shortly moving the mail server capability onto a different server
(server B). Currently all mail for the domains we recieve mail for at
server A is re-relayed through our local server in our office (server C)
where it is delivered. This is done using the following router on server A:

route_myroute:
         driver = manualroute
         transport = remote_smtp
         domains = +relay_to_domains
         route_list = * our.host.name

However, the mail server we are replacing this with will be Debian
stable which only has exim 3.3, and we want to keep the packaged version
rather than install from source. The above configuration does not work
with 3.3, is there some sort of alternative configuration that we can
use, or do we have to install the latest version?

Thanks
Will.