You would need to create a custom pipeline extensibility stage to do this. In theory you should be able to use the setting
<CrawledProperty propertySet="012357BD-1113-171D-1F25-292BB0B0B0B0" varType="31" propertyName="315" />
which is mapped to the managed property "ContentSource". But for some reason this property will not be exported to the custom pipeline stage even though it contains a value. It might be for a reason or a bug, which I'll ask myself in this forum.
So, what are you left to do? You have to use some of the other crawled properties. For example if it's a web crawl you can use
<CrawledProperty propertySet="11280615-f653-448f-8ed8-2915008789f2" varType="31" propertyName="url"/>
and do string checking on the url, and then set your content type property in the output parameter of the stage. I posted a
tutorial on creating and debugging custom stages on my blog post which will get you started.
Regards,
Mikael Svenson
Search Enthusiast - MCTS SharePoint/WCF4/ASP.Net4
http://techmikael.blogspot.com/ - http://www.comperiosearch.com/