NodeJS Sequelize JSON Response for Ember data

I am creating an API for an Ember-App (using ember-data) with NodeJS and Sequelize. I currently have the api returning:

`{"customer":{"id":2,
 "username":"jdsnell",
 "policies":
  [{"id":5,"policytype":"Life","createdAt":null,"updatedAt":null},  
  {"id":6,"policytype":"Auto","createdAt":null,"updatedAt":null}]
 }}`

Generated by the following code:

router.get('/:customer_id',function(req,res){ models.customers.find({ where:{ id:req.params.customer_id }, include: [models.policies] }).then(function(customers){
return res.json({customer:customers}); }); })

I need the response to return only the id's which is what Ember data is expecting, such as:

`{"customer":{"id":2,
 "username":"jdsnell",
 "policies":
  [5,6]
 }}`

How would I go about doing this?