Not possible to extend Vtiger_Widget_Model

I've been trying for hours to generate a custom Widget on a Dashboard which needs a data-sizey="2" parameter.

As my dashboard generator class is in a MyCustomModule/dashboards directory, I stupidly assumed I would be able to extend the Vtiger_Widget_Model in the same way, but unfortunately it seems to be loaded several times during the page load sequence and the initial load, called from Vtiger_Dashboard_Model uses calls which will never use a MyCustomModule_Widget_Model class.

So the only way I can see to do this do this is to modify the Vtiger_Widget_Model class in the getHeight method and add my own Widget title to the special clause so it gets a height of 2.

There doesn't appear to be any way to load an extended class using the normal CustomModule_Name_Model structure.