In Cordova 2.0.0 the cordova.addConstructor() method has been removed. 
But you're right about the global scope. Perhaps a good workout would be to manually create the plugins object in window if it doens't exist (yeah, still global but at least organized), and attach the plugin there. 

For example: 

if(!window.plugins) window.plugins = {};
window.plugins.datePicker = new datePicker();