One easy method is available if the student count is limited -- that of "text" type grades. These are actually grade items you add with a text grade type rather than scale or value. The instructor would need to input the text values for the column but then they would show up on reports and exports.
From programming perspective, all functions having to do with the grader report are in /grade/report/lib.php.
- get_headerhtml() sets up the header for each column
- get_studentshtml() adds the grade values to the cells. When in get_studentshtml() $this->user might contain some of the values you're looking for already ("$this" refers to the report)
- if the values aren't included in the user portion of the object you'll need to go into the function load_users() (also included in grade/report/grader/lib.php) and add the extra values you want