Here's how I solve this:
Send them HALF of the free eBook/report/guide IMMEDIATELY (before they confirm). At this point, if the content is good, they'll want to read the second half...BUT, the second half can only be read/downloaded once they've confirm their email.
I created a new (separate) list within the same niche I was having difficulty in (just for the sake of experimentation), and my confirmation pending numbers dropped by 70%!
The beauty behind this method is that it can work for anything- a video course, audio course, etc. Just give them half of the course immediately, and send them the second half ONLY once they've confirmed their email.
Just wanted to share this useful tip with everyone. See ya!