[Exim] Running Commands

I am struggling with this one!
What I need:
1) When an email is sent to generate_reply@???
2) It needs to run a command (ie /usr/local/bin/generate_reply)
3) This command takes the email message and parses it for vital info
4) this command needs to be run as root.(so it can chown $user) this
newly created files

Is there a way I can set something simple up in /etc/aliases such as:
  generate_reply:    |/usr/local/bin/generate_reply
??
Please help,
Joseph Kezar