Sorry if I wasn't clear ;-)
Currently the upload_file.php adds the list of email addresses as subscribers, without sending them a "Confirm Opt-in" email.
We have many people at conferences and trainings who want to subscribe to our newsletter and manually fill out a paper card to subscribe. Someone on our staff enters those 50-100 addresses into a text file and I upload that list (upload_file.php).
I want to preserve the double opt-in process by having a "Confirm Opt In" email sent to them so they may click on the link to confirm and complete their subscription.
So I read somewhere in the forums that I needed to add that snippet of code to add that function. I just don't know where to find the code that does that.