It's strange to need your data formatted that way. Typically, rows represent different lines of data, while columns in a given row represent different attributes of the same data point.
Since this isn't a native function of the Excel exporter module, I'm thinking you will need to add a custom Java action to transpose the output. This stackoverflow question has some sample code that might get you going: http://stackoverflow.com/questions/5876300/how-to-transpose-sheet-with-poi-ss-xssf
Note: I'm not 100% sure this is the same Excel library that the module uses. I'd recommend taking a peek at the exporter code, and using that same Excel library to operate upon the Excel file output by the exporter module. So, the only change to your export microflow would be one more Java action that takes an Excel file as an input and returns a transposed one.