Maybe I am missing something, but wouldn't the creation of a simple rule accomplish the same thing as the agent you are talking about?
Being a Lotus Notes user who is not on BES, I created a simple rule that forwards all incoming e-mails to my BIS address. When I view the e-mails via my BB, I have all of the From, To, CC, and BCC information (if I was BCCd). When I reply, I simply set my "Sent From" address to my Lotus address (it stays this way most of the time), as well as include my Lotus address as a BCC so I have a copy in my real inbox and no one is the wiser (I know the header will have my BIS address).
Is there an added benefit to the agent you are describing?