In case someone finds this helpful, I use the following stub but it's not tested thoroughly.
```javascript
!function(){
  var Model = Backbone.Model;
  Backbone.Model = Backbone.Model.extend({
      constructor : function(){
        var ret = Model.apply(this, arguments );
        this.isInitialized = true;
        return ret;
      },
      _validate : function(attrs, options){
        var ret, hasOptsValidate = _.has(options, "validate");
        
        if(!hasOptsValidate && this.isInitialized){
          options.validate = true;
        }    
        ret = Model.prototype._validate.call(this, attrs, options);
        if(!hasOptsValidate) delete options.validate;

        return ret;  
      }
  });
}();
```