How to post to create an Ember model under a parent resource?

Let's say I have a parent model which has many children. The REST route for creating one of the children would look like this:

POST /parents/123/children

However, I can't seem to figure out how to set up an ember model to have a parent. It wants to post to /children with a parent_id param. How can I set up Ember so that I can use the URL to identify the parent rather than passing a param?