The only way that I can think of (there may be others) is make use of /etc/mail/virtusertable and/or /etc/aliases. You can control what sendmail does when it receives a mail. See the virtual hosting section on sendmail.org. Wildcards are allowed.
something like that. Check sendmail.org to verify syntax.
What it is doing is when a mail arrives at firstname.lastname@example.org
then the virtusertable looks for "localbob" and localbob resolves to two addresses - bob on the same host and email@example.com