I've implemented this by:
Found this siggraph crytek paper from last year. http://www.crytek.com/download/Playing%20with%20Real-Time%20Shadows.pdf
They are talking about shadows in general and there is a tiny little section about screen space self shadowing that seems to use this technique.
As a screen space technique it's not a drop-in replacement for regular shadow maps, really just an addon to increase fidelity.
1) Implement SSAO the kind that uses random world/view-space points on a hemisphere/sphere around the pixel being shaded.
2) Take the code that finds sampling points on this (hemi)sphere, and change it to instead generate points along a line towards the light source.