Use Anaconda's Python distribution within OSGeo4W

I want to use a Python script that executes Grass commands via os.system(). This of course, has to be executed from a running Grass session. However, when I use the OSGeo4W Grass, it does not find all imported packages as it falls back to its own/default Python distribution. How can I enforce OSGeo4W to use the Anaconda Python distribution?

I found a solution on the internet that makes the OSGeo4W distribution available systemwide, but not the other way around. How is it possible to do that?