Add Column to Row Report that was not in original sheet


I have created a Row Report containing information from just one sheet, with one "What?" criteria.

I have the desire to add another column to this report, that does not come from the original sheet, just for notes purposes. This column would have sensitive information in it that I do not want the other owners of the original report to see or have access to.

Is there a way to add a new column to this report that does not come from the original sheet? Or are there any work around for this that people have found?