I ended up using Django Signals. With a flat table "item_record" containing fields "item" and "description", the code in models.py looks like this:
from django.db.models.signals import post_save
def create_item_record_history(instance, created, **kwargs):
if created:
ItemRecordHistory.objects.create(
title=instance.title,
description=instance.description,
created_at=instance.created_at,
)
post_save.connect(create_item_record_history, sender=ItemRecord)
It is running well for my purposes. Although it's just creating an annotated flat table (new field "created_at"), the same method could be used to build out a star schema.