partly readonly

hi
i want to make the fckeditor partly readyonly is it possible to do that.
well what i want to do is after reading data from db the edit area of the editor should be readonly except for a particular tag called <<FREETEXT>>.
i want the user to only edit these tags in data fetched from the db (the user should not be able to edit anything else).
i would be greateful of any suggestions

thanks
sa