Have to say, Otto has a point. My MSc supervisor did her PhD by publication. It's a field where the department has a few lecturers without PhDs as it's heavily reliant on practice/industry expertise.
Even with 15+ years working in the field, and nearly 20-odd publications, she found it hard. hard because it too a back seat alongside other things and because it's difficult bringing many publications together under one "roof".
It's not the kind of thing that you can do "on it's own" if that makes sense. The only people I've ever known who've done it are existing members of an academic department (as Jewel points out) and they have other duties - teaching, other research projects, administrative duties etc. Unlike studying for a PhD where it's pretty much the main thing in your life, a PhD by publication is more "sidelined". At least that's the impression I get...