The only way to do this is to programe an agent on the server. It will track the message with specifid subject, or message or user as you want and forward it to where you want it. It will be a real forward. But this is not native in Domino you need to write the agent in make it run on the server. It is not verry long to do probably .5 a day.
I would like to just further add to the above comment. While what is stated is true, another option would be to use the COM interface provided by Outlook in a “Before Mail Arrives” agent, and just drop the email in the Shared Folder programmatically.