[Python] How to use a post_save receiver with django-polymorphic?

I have a django-polymorphic model and want to implement a post_save signal to automatically create a related model that is also polymorphic.

It's something like the code below, the relevant piece of non-working code being the @receiver decorated work_post_save method. The problem is the instance is a ctype_id and not an object.

from django.db import models
from django.db.models import signals
from django.dispatch import receiver
from polymorphic.models import PolymorphicModel

from mygallery.models import Album

# Work Parent PolymorphicModel
class Work(PolymorphicModel):
title = models.CharField(blank=True,max_length=256)
slug = models.SlugField(max_length=256)

@receiver(signals.post_save, sender=Work)
def work_post_save(sender, instance, signal, created, **kwargs):
album, new = Album.objects.get_or_create(title=instance.title + ' Stills', slug=instance.slug + '-stills')
work_album, new = WorkAlbum.objects.get_or_create(work=instance, album=album, is_key=True)


class ArtProject(Work):
manifesto = models.CharField(blank=True,max_length=256)

class CodeProject(Work):
code = models.CharField(blank=True,max_length=256)


# Content Parent PolymorphicModel
class WorkContent(PolymorphicModel):
is_key = models.BooleanField(default=False, unique=True, default=False)


class WorkAlbum(WorkContent):
work = models.ForeignKey(Work, related_name='work_albums')
album = models.ForeignKey(Album, related_name='album_works')

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