I found a workaround for now.
This process works to send email with a CC found in another BO attribute:
LoggedInRegularUser.ListLineCCs=LIST_LINE('EmailCCs','',';','EmailAddress')
CREATE OutgoingEmail_Test WITH OutgoingEmail_Test.CC=LoggedInRegularUser.ListLineCCs
SEND OutgoingEmail_Test TO RegularUser
(EmailCCs is a query with: FIND EmailCC WHERE EmailCC.ShowInCC='Yes')
Note that it stores the results of the LIST_LINE function in a LoggedInRegularUser attribute, then uses that attribute to populate the CC attribute of the email notification.