crm 2011 plug-in callerorigin

I've foundout callerorigin is removed from 2011.

Is there a way in the plug-in to identify who triggered the plug-in like web application/WCF etc.

We have a scenario where the web app does validation before it calls the plugin.

So in the plugin we dont want to double validate if it's coming from webapp, only if it is coming from CRM UI we want to do the validation.