Set `options.attrs` will allow you customise api param

customise-backbone-save-api-param.js

// when model.attributes is different from the params to save
// e.g. when save to restful api, one attr should be `resource_uri` 
//   formated as string type, but the returned attr value in json is object formated
var model = new Backbone.Model();
model.save(null, {
  wait: true,
  success: function() {
  },
  attrs: _.omit(model.attributes, 'selected')
});