I'm not invading anyone's space.
Yesterday, I was hanging out on Oxford Street, people watching. When someone came along who I thought I'd like to work with, I was just asking for a moment of their time. I explained to them who I was, what I was doing and how they could find their portrait if they agreed to be photographed. It was all very friendly and I reckon I had as many rejections as I had people who were happy to help.
Admittedly, this isn't an activity for the socially awkward, but then one of the aims of the project is to increase your social skills as well as your skills as a photographer.
Oh - and Mike, FWIW I think that your approach is every bit as hard core as mine. My subjects have zero expectations of the images that might result from their time in front of a lens. The people you've been working with want to see something for their time and they almost certainly expect a certain standard of work.
Loving your site, by the way. Expect to see mine any day soon