Blending for non-Camschnappr cameras

Is there any way to use the Blending mask shader of Camschnappr for standard cameras?

I am working at the mapping of a dome-shaped roof using 8 projectors.

My first try was to use Camschnappr for the camera calibration, but it always gives me a black render view, so I´ve decided to place the camera manually (I have the measures and the info about the projectors) and add some warping with Stoner.
I can achieve a good allignement this way, but now I need to blend the projectors, so I am trying to adapt the blending part of Camschnappr to work with standard Cameras to calculate the masks.