How to (Painfully) Do It Anyway

Find PYZ-00.pyz in _MEIPASS (for one-file mode) or dist/yourapp/ (one-folder mode).
Extract it manually using pyi-archive_viewer:

pyi-archive_viewer app_name.exe

Load .pyc files manually using importlib.util:

import importlib.util

spec = importlib.util.spec_from_file_location("mymodule", "extracted/mymodule.pyc")
mymodule = importlib.util.module_from_spec(spec)
spec.loader.exec_module(mymodule)

print(mymodule.some_function())

Cry and question life choices.