Third-party import from local folder

I have to have external package locally because it is rapidly developing. So I included it in my project as git submodule. In PyCharm I had to mark it as  Source Root. When I use `cmd+opt+L` to automatically reformat my code IDE puts imports alphabetically. 

How I want my import to be sorted:

from common import that_func  # external package

from best_package import Best # my package

What I get:

from best_package import Best # my package
from common import that_func  # external package

Is there any way to mark some local folders as third-party package, so IDE could treat it properly?