Converting to Custom User Model (Django 1.5)

[PRyan]

We are currently using the following user model setup:

settings.py:

AUTH_USER_MODEL = 'auth.User'

userprofile.py:

class UserProfile(DirtyFieldsMixin, User):

Is it possible to change these to the following and have South take care of the data as not lose anything?

settings.py:

AUTH_USER_MODEL = 'userprofile.UserProfile'

userprofile.py:

class UserProfile(DirtyFieldsMixin, AbstractUser):

I have looked through here and the rest of google and all the answers show created a new custom user that you copy everything to. Is it possible to continue to use our UserProfile but just convert it to extend AbstractUser as made possible in Django 1.5 (which we are currently using)?

Thanks!