[exim] Routing based on added headers.

Hi All,

Before I drown myself in an overcomplicated solution, I thought
I would ask the community.

I have a number of simple aliases via a redirect router, a la
an /etc/aliases file. I'd like to be able to have a
"Precedence: junk" header added to some of these so they can
be considered as junk.

The goal would be so that later routing via autoresponders
could ignore the message (for example, so a vacation response
would not be generated).

I can't just add the Precedence: header in the redirect router
since section 43.16 of the docs says the added headers will not be available
to later routers.

Since these are relatively simple aliases, I would prefer
not to go down the road of setting up something like
mailman.

Does anyone have any simple suggestions for doing this? I'm
probably missing something obvious.

Thanks!
Tom