I've not tried building a spreadsheet with drop-downs in it before. But when I try to do anything special in a spreadsheet, I'll often make one by hand and take it apart with Spreadsheet::ParseExcel to see what kinds of things I need to do. (It doesn't always work, as Spreadsheet::ParseExcel isn't perfect, and Spreadsheet::WriteExcel doesn't always have the method I want. But I've been generally successful.

On the cases where I've not been successful, I've saved the spreadsheet in XML format and perused that for clues. (As in, I wonder if the drop-down is signalled by a special formatting code, or some such...)

When even that doesn't work, I cop out and write a spreadsheet template that reads its data from a data source (database, CSV file, etc.) and populate the data source with some perl code.

...roboticus