Yes, it would be nice if Vue had an object intersection node which could calculate the the intersection profile of 2 objects which in turn could be used to drive the foam,  Usually I add another fractal node in combination with the distance to object below node in order to make the foam less uniform.   The other possibility with Vue 7.4/7.5 is to paint the foam edge in the Terrain Editor - kinda like your Photoshop technique Art Pearl.