Changing the orientation is just switching column and row indexes. So, probably you can use something like this:

private void DataPresenterExcelExporter_CellExporting(object sender, CellExportingEventArgs e)

        {

            e.Cancel = true;

            int row = e.CurrentRowIndex;

            int col = e.CurrentColumnIndex;

            e.Workbook.Worksheets[e.CurrentWorksheet.Index].Rows[col].Cells[row].Value = e.Value;

        }

This seems to only control printing. It doesn't affect how the export occurs. Back to square 1... Has anybody been able to export a horizontally-oriented XamDataGrid to Excel and have that horizontal orientation retained in the spreadsheet?