How to save nested objects in ember js

In a related question I wanted to know How to add parent object to child in a one-to-many relationship in ember.js. Now I want to know how to simultaneously save them on the server when creating or updating the parent with a newly created child.

The server would expect something like this:

parent {
    prop1: 'val1',
    prop2: 'val2',
    child: {
        prop1: val1
        prop2: val2
    } 
}

but ember's payload looks like this:

parent {
    prop1: 'val1',
    prop2: 'val2',
    child:null
}

The same goes for updates when having an already existing child appended to the parent. Then the payload looks something like this:

parent {
    prop1: 'val1',
    prop2: 'val2',
    child:2
}

So it's not the child-object transferred with the payload but only it's id if existing (otherwise null)). Is it possible to send a nested object like the server expects or do I have to save both models separately with two ajax-post/put-requests.?