(2D) Outline shader applied to particles as a whole and not individual particles?

I have an outline shader that I made (ok, followed a tutorial and improvised a bit) that I would like to apply to a particle system, but I'd like the outline to be around all particles as a whole when the particles are overlapping each other. Basically, this -



This is the shader I am currently using -



Could something like this shader be adapted to the above? I'm trying not to resort to using one of those fluid simulations, as that would require using a lot of game objects.