[exim] block whole domain except for a few rcpts

I would like to know the easiest way to do the following, which I guess
is some sort of selective relaying.

I want to block a whole domain, say example.com.
But I would like email for rcpt1@??? and postmaster@???
to pass through and be relayed to the MTA of that domain.

I already have functionality to deliver email to the specific domain
(debian's hubbed_hosts). It just needs to be done not for the whole
domain but selected addresses. Ideally the address should be read from a
text file, one address per line.

Thank you,
Jeroen