[Exim] Dynamic helo_data based on outgoing IP?

Hello,

Is it possible to make "helo_data" option for smtp transport match the
name backresolved from IP that we are making outgoing connection from?

Suppose, we have a host with 2 interfaces:
1: 10.0.0.1 that backresolves to "host1.domain1.fake",
2: 10.0.1.1 that backresolves to "host2.domain2.fake"
Suppose also that $primary_hostname for this host is "host1.domain1.fake"
that resolves to 10.0.0.1.

Now, if our outgoing SMTP connection originates at 10.0.0.1, the default
exim HELO host1.domain1.fake matches this address perfectly well and
everything is OK. But when our outgoing SMTP connection originates at
10.0.1.1 (e.g., because of changed default route) the default
HELO host1.domain1.fake would fail exim's own helo verifications.

Since helo_data is expanded string it may be pretty possible to implement
the above behaviour in case there is some variable holding our outgoing
IP address. Unfortunately, I was unable to find such a variable in the
docs.

Any ideas?

--
Olwi