Well, one quick method would be to put fake email addresses for the users you don't want to receive any notifications. This way you can right away stop any communication with these users, no matter what extension would be involved.
To add such a feature to profilebook plugin would involve code changes.
The other extensions you mentioned have nothing to do with CB (Docman, SOBI) so they would also need to be modified as well.
Sorry, CB was not designed to be a CRM.