How do I access my model's custom manager in a Django data migration context?

I have a custom model manager used in several of my models. This manager helps speed up DB inserts. I need to perform a data migration, and it involves migrating several millions of records/objects. I need my custom manager in my data migration. Does anyone know how to get it. In the data migration context if I run model.objects this gives me back Django's model manager.

As of now the approach I am using, and which seems to work reliably is to instantiate a local Manager for the model, then set manager's model attribute to the model I am interested in:

class MyManager(Manager):
    ...
    def my_create_func(self):
        ...

class MyModel(Model):
    ...
    objects = MyManager()

def data_migration(apps, schema_editor):
    model = apps.get_model(...)
    manager = MyManager()
    manager.model = model
    manager.my_create_func()