narashima,

Not a complete Perl soultion but..
Could you not have your pivot table in an Excel sheet**, then append the output from your Perl script to the file?

**If you pre define a piviot table you should be able to update it when the excel file is next opened using a VBS (within the Excel file, NOT your Perl script) like:

Sub Auto_Open()
Application.OnSheetActivate = "UpdateIt"
End Sub

Sub UpdateIt()
Dim iP As Integer
Application.DisplayAlerts = False
For iP = 1 To ActiveSheet.PivotTables.Count
   ActiveSheet.PivotTables(iP).RefreshTable
Next
Application.DisplayAlerts = True
End Sub
[download]

Please excuse the fact that this is not Perl code :(
Are you currently able to write data to an Excel file? Cpan has many modules regards Excel writting.

Hope this helps.

Martin