Saving two new related objects in one request

I have two models in Django:

class Thread(models.Model):
    entity = models.ForeignKey(Entity, null=True, blank=True)
    ...

class ThreadMessage(models.Model):
    thread = models.ForeignKey(Thread, related_name='messages')
    author = models.ForeignKey(User)
    ...

Now a client wants to create a new thread with first message in it. It has first to do a POST /threads to create a new thread and find out its id and then do POST /messages passing the found id in thread field.

I am thinking if it's reasonable and possible to do all of this in one request from Ember like:

POST /messages 
{"message": {"text": "text", ...},
 "thread":  {"entity": 1}}

And the response would be:

{"message": {"text": "text", "id": 5678, "thread": 1234, ...},
 "thread":  {"entitity": 1, "id": 1234, ...}}