Unfortunately, we users can't do this, as we cannot edit that script.
What is supposed to happen is that, once a new domain is added to the DreamHost DNS listings, it is added to the referrers' array "automagically" (usually in about a day).
Is it possible that this is a "newish" domain?
You can always generate a support ticket, and see if they can troubleshoot it for you, though if the domain is "new" to DreamHost, it should sort itself out in about a day.
Of course, in the meantime, you can always use your own script. The NMS formmail referred to in the error message, which is the basis for the DreamHost script, is free and readily available.