Location for custom python stubs?

Does PyCharm have a default location for custom python command stubs for code completion?

I've generated custom stubs for a swig wrapped api I'm using across multiple projects, and would like to use this for code completion hints. The only way I have been able to get this working so far is to add the root folder for my command stubs as a content root for my project, and then exclude that folder so it doesn't show up in my project files.

This seems less than ideal, and has to be setup per project. This method also messes up my import code complete prompts.

Ideally, there would be a global (project agnostic) location I could place these stubs that the editor would use for code completion.
I've tried adding the stub files to my ~/.PyCharmXX/system/python_stubs/ folder, but this doesn't seem to work...

Is there any existing mechanism to get this working? Thanks.