How can I `import *` from a module loaded with imp?

I currently work with keras and custom activation functions. I store those models as pickle and I would like to be able to load them again. Then I run into this issue.

The problem is that the Python script which contains the custom activation function is given by path. I load this script via

import imp
model_module = imp.load_source('model', experiment_meta['model']['script_path'])

How can I "star import" (import *) in this case to make the loading of the trained model work?

What I've tried

from model_module import *

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named model_module