[exim] virtual users in MySQL - how to do offsite forwarding…

I'm planning exim with virtual domains/users in MySQL database. I've
installed a quick pilot and mail delivery for virtual users works.

I need to implement offsite forward with local copy (some people want to
get copy of incoming message delivered to address in different system.)
How do|would you implement this feature with virtual users in MySQL?

(Also what do you think is best way to implement aliases for user
addresses?)

For delivery to virtual users I'm using following construction:

  virtual_user:
      driver = redirect
      allow_fail
      allow_defer
      data = ${lookup mysql{ SELECT maildir FROM users WHERE id='${local_part}@${domain}' }}
      directory_transport = address_directory

and

  address_directory:
    debug_print = "T: address_directory for $local_part@$domain"
    driver = appendfile
    delivery_date_add
    envelope_to_add = true
    return_path_add = true
    check_string = ""
    escape_string = ""
    maildir_format = true
    mode = 0600
    user = mail
    group = mail

Thank you for your tips and hints.

Vit