[Exim] A router entry request

Dear list,
I am new to Exim and have been pouring over the docs for a while
but don't see how to do the following.

I have read Q0320 and it's answer in the FAQ regarding blocking
all email being sent from the 'nobody' account on a virtual server.
The answer states that I need to set up a router with
senders=nobody@??? which routes all mail to a local
transport that delivers it to /dev/null.

The problem I am trying to solve is that there are many accounts
on my server running various scripts and it seems that there are
some sending out emails from 'nobody@???' and I get
multiple complaints each day about these messages. I have searched
for the offending scripts and have been unsuccessful so far.
This router seems to be the way to stop this behavior until I can
determine the root cause.

What I don't know how to do is create this router from scratch.
Can anyone provide the necessary router section I need to add to the config?

Is this routers placement in the config file important or can it just go
at the end of the existing routers?

Also - (probably a stupid newbie question) - will I need to compile the
program after making this change or will it be effective by restarting Exim?

Thank you in advance,
John A. Buck
Maximum-Mail Web Hosting Services