Outgoing Mail filter - w/ ASSP or Exim

Hi All, Ive been looking around on forums for an answer to this - without luck, hopefully somebody can advise if this is possible! A client has asked to block emails sent to a particular domain completely from his cPanel account. To clarify - any email sent from all email accounts on the clients domain, eg john@clientdomain.com or sam@clientdomaincom sent to fraud@acme.com or account@acme.com etc, needs to be prevented from sending - ideally with a bounce message of some sort. There is a good reason the client wants to do this - but I wont go into details as its complicated. I am running the latest release of WHM/cPanel, with Exim and ASSP installed. Any suggestions would be greatly appreciated!