While there's no "append" functionality for Excel out-of-the-box, you could try the following:
1. Save your Excel document as a .csv file (or copy the Excel file to a .csv file)
2. Use a Append Lines to Text File component to append new comma separated data to the CSV file.
3. Use a Write File component and write the appended file back as a .xls file..
If your Excel file is pretty basic, this should work.