Ember Relationship with different ID Key

How can I use Ember Data using a different ID key then it's expecting? For example; If I have a profile, tied to a user account, Ember expects this:

{
    id: 44,
    name: 'Some Name',
    phone: 555-555-5555
    user: 24
}

How can you change Ember to look for the model with an underscore and ID?

{
    id: 44,
    name: 'Some Name',
    phone: 555-555-5555
    user_id: 24
}