var BodyView = Backbone.View.extend({
  initialize: function() {
    this.listenTo(Backbone, 'prevent-scroll', this.preventScroll);
  },

  preventScroll: function(prevent) {
    // .prevent-scroll has the following CSS rule: overflow: hidden;
    this.$el.toggleClass('prevent-scroll', prevent);
  }
});

// And now from anywhere in the code:
Backbone.trigger('prevent-scroll', true); // prevent scrolling
Backbone.trigger('prevent-scroll', false); // allow scrolling