I agree that using a name rather than an object reference not only seems more consistent, but is actually what South typically utilizes. It's an interesting case.

Though, what I added in this pull request is what is being utilized in a bunch of different projects for adding Django 1.5 support.

Here is one discussion on this: http://stackoverflow.com/questions/15472704/trouble-migrating-reusable-django-app-models-to-use-a-custom-user-model

I have also seen this tactic be in use: https://github.com/frankwiles/django-app-metrics/pull/35/files