[Exim] local mail amongst smarthost queue

I have an Exim 3.34 smarthost machine that delivers email that
originated from other machines.

The machine itself also generates some email messages that need to be
delivered to external machines. I want that email to go out via a
different transport than the email being relayed.

It seems that I can identify the local mail by the $originator_uid
string expansion variable, and that I could build a condition to
identify the locally generated email that way.

Is there a cleaner and/or better way of identifying this email in Exim 3 ?

Thanks for any tips.

mark