It is already requested as an enhancement and it is tracked with "Bug 9308736 : ER: OVERRIDE EMAIL ADDRESS FOR RECIPIENT MISSING FOR EMAIL DELIVERY"..
However; there is no fix yet.
As a short and sharp wokaround, you can disable mail server access of your cloned instance..
But, this will prevent all the mail server related activity/tests that should be done on your cloned instance.
So.. If disabling the mail server acess is not a valid workaround for you; you may try the method given in the below link .. It is a little tricky but looks good.
http://piotrbelter.blogspot.com/2015/05/email-override-for-concurrent-request.html