I have started with a render with the standard colorisation below




Set the brush as above and brush across the area required for general volume lighting similar to that shown below.



Apply Filter > Blur > Radial Blur Zoom 100%. The result should be similiar to below




using the above eraser settings. Lightly brush over the lighting like the image below



Apply Filter > Blur > Gaussian Blur radius 2.5.




Using the above settings for the lasso tool while holding shift select from parts of the render as shown below.




Now simply delete these unwanted areas from the volume light area.



Here is an example of it in use.




Important note: The author is not a natural English speaker and there is a high chance of mistakes in every way. Corrections and comments are welcome.