Lists sharing membership?

Hi! I have a mailing list which is configured to send all replies back  
to the list, to promote discussion (well, as many replies as Outlook  
will allow). I've been asked to set up a second list, with exactly the  
same set of recipients, which is for annoucements only, where the  
replies go back to the sender. Is there any way to create a list which  
is never actually subscribed to, but grabs its subscribers from a  
different list? This would have to be dynamic, as the original's list  
membership changes from time to time as study investigators and  
project managers come and go, and I'm trying to avoid just having a  
second list that we have to remember to subscribe people to.

Thanks,
Ricky

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