Spreadsheet::WriteExcel indeed does have a write_comment() method. Unfortunately version 0.42 (where write_comment() works) uses an old Excel version and cannot support cells with more than (I think) 256 characters. The newer version 2.01 uses Excel97 format and allows more text in cells but the write_comment() method is inactive.

Spreadsheet::WriteExcel is a great module but some of these quirks still remain. I have never tried Win32:OLE