Adding support for PYTHONPATH for Python scripting

Is it possible to add support, or inclusion, of the environment variable PYTHONPATH to add module/script search paths?

Like the OCIO environment variable for setting color space definitions, usually we will add a path to the PYTHONPATH variable, Linux or Windows, and Python generally picks that up, adding those paths to the sys.path list.

Would this be possible? Or is there an already built in variable we can set? Or am I missing an obvious setting that needs turned on? Having tried: BLENDER_USER_SCRIPTS BLENDER_SYSTEM_SCRIPTS BLENDER_SYSTEM_PYTHON But they didn't seem to do the trick.

This would be a great feature addition. Correcting me on something being missed is a huge welcome also.