Outlook Tasks appears the only way. Follow up flags do not work with BCM so
you will need to use Tasks.

Bear in mind that creating a Task will not automatically allow a drill
through "to and from" the account or contact record you need, so you will
need to manually create a link if you want this capability. i.e. when you
create a new Task, go to the Contacts box (bottom left), browse to the record
to attach it to and Save.