How do I move mails sent from me on behalf of someone from my sent items mailbox to their deleted items mailbox folder?

I have full access to my manager's mailbox.  I am able to send mail on his behalf.  
He wants to be able to see the mail I have sent on his behalf.
When I try to move the message from my sent items to my manager's deleted items- the mail goes to my deleted items.

I then have to drag the mail from my deleted items to my manager's deleted items before it appears there.

Is there a work around for this?
I do not want all my sent mail to be copied to my manager's deleted items.  I only want mails that I send on his behalf to be moved to his deleted items.

Any help would be greatly appreciated.

Many Thanks.