How do I precompile a submodule?

I maintain a Python package and I want to precompile code with Numba.
The precompiled code should live in a submodule of that package in order to not pollute the global namespace.

For reference, the package mytestpackage could look like this:

from setuptools import setup, find_packages
from numba.pycc import CC

cc = CC("shouldbesubmodule")

@cc.export("foo", "void()")
def foo():
    print("Hello, World!")


And I want to be able to import the submodule like import mytestpackage.shouldbesubmodule

python3 install
cd /tmp
# this works:
python3 -c "from shouldbesubmodule import foo; foo()"
# but I want this to work instead:
python3 -c "from mytestpackage.shouldbesubmodule import foo; foo()"

I thought that maybe this could be as easy as specifying the package in the call to CC similar to cffi:

cc = CC("mytestpackage.shouldbesubmodule")

but that does not work because dots are explicitly disallowed in that string.

Changing the Numba source code here to ext = _CCExtension(name="mytestpackage.shouldbesubmodule", works, but I would like to be able to do that without modifying the Numba source code.

The CC-Object has a parameter source_module, but if it is intended for this use case somehow, it is not clear to me how to use it.

In conclusion: How can I precompile a submodule shouldbesubmodule for a package mytestpackage so that import mytestpackage.shouldbesubmodule works?

Apparently, things “just work” if the cc-Objekt is imported from a submodule instead of being created in