Oh gosh, I know this was a while ago, but are you OK now?
A self-shadowing blueprint light source sounds pretty awesome! Also, Daniel W. commented on that POM thread, saying a Pixel Depth Offset material node is coming in UE 4.8: this will allow you to push pixels back into the screen, making post-process Ambient Occlusion possible. If you can use it, this will be huge.
Sorry, I tried to find a better solution than a simple fresnel falloff, and I just couldn’t. I tried pixel depth, a combination of pixel depth and fresnel, and even just hard-coding the samples, but nothing improved performance better than fresnel by itself: more samples at oblique angles, less samples when viewed head-on. I think the reason for this is the majority of screenspace for a material like this will be viewed head on, and only a small portion of the screen will glance the edges. Also, the instruction count is much lower than if you wanted to combine another distance-based system to eliminate ridiculous sampling in the background. Even one extra instruction performed worse than simply allowing the samples to accumulate in the distance. You can still try your own solutions, though.