[exim] multiple pgsql servers for different purposes

My current setup ported from my old server uses a pgsql connection to our
internal web server for multiple purposes including email to helpdesk and
other facilities.

I now want to add another pgsql database on my mail server specifically for
improving EXIM's handling of emails.

Looking at the docs it looks like I can't do this as multiple servers can only
be specified for backup purposes.

Am I wrong? Is there any way I can direct lookups to a specific pgsql server?