Tell me I'm just not looking in the right place.
Is there not the option to add a field to a report after it has initially been created? I'm not talking about a dynamic text element with a field value in the report- I'm talking about the list of fields specified when the report is created. I neglected to add a specific field that I now want to use to sort the report (Report Properties->Sorting) and since that field isn't in the list, I can't sort it on that field.
Right now, it appears to me as though I have to make the report from scratch which seems absurd. Changing the Data Source (Report Properties->Source) offers no options about fields.