class PrefetchWorkaroundManager(models.Manager):

    def get_queryset(self):
        q = super(PrefetchWorkaroundManager, self).get_queryset()
content_typeA = ContentType.objects.get_for_model(ModelA)
content_typeB = ContentType.objects.get_for_model(ModelB)
return q.filter(content_type__pk=content_typeA.id).prefetch_related(
    'content_object', 'content_object__event_object') | q.filter(
    content_type__pk=content_typeB.id).prefetch_related('content_object',
    'content_object__event')


class ModelC(models.Model):
    pass
Multiple fields to the same DB column