https://github.com/PaulUithol/Backbone-relational looks like a cleaner approach. It relies on the same basic stuff, a model store to keep track globally of model instances.

Example in coffeescript:

this.Foreman = Backbone.Model.extend
    initialize: -> 
        # will add a projects attribute to the foreman and a foreman attribute to the project
        _.extend(this, new Porkepic.HasMany(this, Project, "projects", "foreman"))
        # will add a worksheets attributes to the foreman
        _.extend(this, new Porkepic.EmbeddedInMany(this, WorkSheet, "worksheets", "foreman"))

    url : -> "/users/" + this.id