http://email.about.com/od/macosxmailtips/qt/et_auto_bcc.htm

2nd:


Select the BCC Myself option. Then, in Rules:
Select "Any" (If ANY of the following conditions...); select Account (your own that's being BCC-ed).
Under "Perform the following actions", select Forward Message; then fill in your secretary's email address after To. 

If this doesn't work with Account, try selecting "Sender is member of group" and create a new Group in AddressBook where only your BCC address is listed.

It's a kind of work-around, if not a run-around, but worth a try.