Ember: create a DS.belongsTo *outside* of a Model

I'm wanting to ideally create a DS.belongsTo / BelongsToRelationship in my own class (which is an Ember.Object, but not a DS.Model), or alternatively recreate the functionality to let me hold a reference to a record in my own class. I don't know if it's possible to use a DS.belongsTo outside of a DS.Model, or if so, how to set it up.

Background:

I have an ember-cli app using ember-data + ember-fire + firebase. One of my models has an attribute which is an object holding "type specific" information for the record. I transform this object into my own class based on the type it describes, and some times that type will have references to other records in the database. In these cases I would like to have a DS.belongsTo property set up in my typeSpecific class that I could link to in the same way as linking to a relationship in a regular model.

Alternative:

After a lot of searching and not finding any information on how to do this I made my own class which got me most of the way there. I've just noticed that although I can change the record it references on the client side and have it update, if I change it on the server-side I don't get updates coming through, so it's back to the drawing board.

If anyone is able to tell me how to make this alternative approach work that would serve the purpose too. The idea with this class is that I pass it a model name and id, and it should create the model reference and then keep model and id in sync if either side changes, and also pass through updates if anything on the model it's connected to gets changed just like a regular relationship would.

export default Ember.Object.extend({

  id: null,
  table: undefined,
  model: undefined,
  store: undefined,

  init: function() {
    this._super();
    if(this.id && !this.model) {
      this.updateModel();
    }
    else if(this.model && !this.id) {
      this.updateId();
    }
  },

  updateModel: function() {
    var self = this;
    if( this.get('id') ) {
      this.store.find(this.get('table'), this.get('id')).then( function(model) {
         self.set('model', model);
      });
    }
    else {
      self.set('model', undefined);
    }
  }.observes('id','table'),

  updateId: function() {
    if(this.get('model')) {
      this.set('id', this.get('model.id'));
    }
    else {
      this.set('id', null);
    }
  }.observes('model'),
});