You could just pay for GitHub to get private repos. If it's something this important to you, it's probably worth a few bucks a month.
This solution is also strange because if you ever committed anything private it will be in the history. So to make this work you either have to rebase over some history, or lose all the history.
I have a lot of private repos. One for just about every little project I've done. Some larger projects have more than one. It would be pretty expensive to keep all of this in Github that way. The alternative is to combine a bunch of unrelated stuff into fewer repos (or not keep all of my projects in source control), neither of which is especially appealing.
I'd be happy to pay Github something for my usage and to support development. I believe in paying people for work that I find useful. But the pricing model makes the cost disproportionate with the value for me.
This solution is also strange because if you ever committed anything private it will be in the history. So to make this work you either have to rebase over some history, or lose all the history.