Using polymorphic queries over interfaces in RavenDB

I'm interested in switching over our application (or parts of it) to use RavenDB from SQL server with NHibernate.

The key feature that I can't seem to find in Raven is the usage of interfaces for queries eg:

ISearchable
{
  string Name {get;set;}
}

Class1 : ISearchable
{
  string Name {get;set;}
}
Class2 : ISearchable
{
   string Name {get;set;}
}

In NH I can search for the contents of the Name field in any ISearchable: QueryOver<ISearchable>().

I can't seem to find this in Raven, am I missing something? The closest that I've found is changing the string part at the front of the identifier, which I don't want to do; the main function of Class1 and Class2 is not to be searchable!

Thanks

Stu

Define an index like:

// ByName
from doc in docs
select new { doc.Name }

session.Query("ByName");