Adding external e-mail addresses to a Mail Merge

Hi,

While working with the Bulk Mail Merge feature, is it possible to add external entries to the recipient list of the message?  For example, we have a list of users and e-mail addresses tied to users of our online software.  When we do updates, we want to notify all the users of our changes, but we don't really want to add them as contacts (the list would be large, as each admin user of our software can add other sub-users under them).  Can we modify the list of the bulk mail merge and insert all these users and e-mails into