I am not sure if it is even possible with this type of render to implement such thing, but some alternative to vray's sphere fade (atmospherics) would cut down on render times. (at least in theory it does)
in combination with render to texture it would drastically cut down on render times for animations.
imagine this:
big scene with mainly static objects and only few dynamic objects (transparent, moving etc).
render to texture would take care of diffuse, shadows...
sphere gizmo with spehere fade would take care of dynamic objects
and some simple aproach to get speculars and reflections