Put another way, he accepts a portfolio of projects (github, pro-bono work, etc.) that demonstrates skill/drive in lieu of previous employment.

Yeah, that's called experience.

Right, but that is different than paid experience, which is what the OP was talking about.

Among my specific gripes is that most employers don't regard open source projects as experience, because I'm not paid to contribute to them.

I'm not saying that there aren't ANY employers who respect unpaid experience, just that they are uncommon.

Quite commonly I offer to provide sample source for programs I've actually written. No one ever wants to look at my source - they only want to know that someone else has paid me.