The ways of doing this in Perl are pretty much identical to that of any other language, since the underlying subsystem is OLE. You can directly reference any sheet in the workbook without affecting the user-interface (e.g. by activating or opening the sheet), and you probably don’t want to except to “put on an I’m Busy Show” for the end-user. You can reference the elements in any Collection (such as Sheets either by index or by name. Again, the principles and modus operandi are the same everywhere. Learn how to do it first (say, in Excel’s own built-in VB/macro facility), then translate the known-good methods into Perl-talk.
Incidentally, I am of the opinion that “when in Rome, do as the Romans do.” In the Windows environment, that’s OLE. It works, and it works quite well. Much better, IMHO, than trying to build a file.