In the version 1.9.0 we add a new blend mode.
We watch the interesting video that you have shared, we discover that to simulate the Blizzard BlendAdd effect, we should work with a 2 pass shader.
It's possible to do it be we need extra coding, Blizzard use is how engine and we beleive that is more flexible for them to recreate this shader.
We need to work around it, but your request is available :)
Best Regards,
Vetasoft