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