It's been awhile since I went down this road but doesn't is still show up in the task bar? Sure it's more than one key stroke or if you are an 'alt-tab focus' person then that, but my recollection (and personal frustrating experience) is that the application is still running in a keystroke/mouse accessible way to the user. For any long running parsing your risk of clicking on Excel goes up especially if you use Excel for other purposes.
This wasn't really part of my initial answer but the other risk of using Win32::OLE is that you have available both read and write capabilities for the file. In general this won't be a problem but you risk the case where you overwrite data before you have read it.