code: function(filter) {
  		this._startLatLng = filter.northEast;
  
  		var shape = new L.Rectangle(new L.LatLngBounds(this._startLatLng, filter.southWest), this.options.shapeOptions);
  		return { type: 'rectangle', 'layer': shape };
  	}
docs: Programmatic way to draw a filter rectangle (bit of a hack)