masking light output in a shader for a 2d game

I am currently playing around with the asset 2D Dynamic Lights and Shadows

and I was wondering how hard it would be to make it so that the shadow would mask out another lighting shader I am using so I would get this:

Does anyone think this would be possible? or am I just going to have to re-write my other shader to only render light pass if within the light.

I understand this would be probably hard to answer without seeing all the code. so if anyone could just point me in the direction of masking lights and or only applying lights over a certain area determined by an ingame mesh (my shadow mesh) that would rock.

Thanks