search with pattern

I am attempting to search for

using (var context = new $DataContext$())

where DataContext is any class that extends

System.Data.Linq.DataContext

using Resharpers 'Search with Pattern'.
The pattern I'm using is:

using($type$ $var$ = new $type$($args$))
{
  $stmt$
}

This appears to return all using statements, eg using StreamWriter, using FileStream, things that clearly do not derive from

System.Data.Linq.DataContext

How can you return only the types indicated?
I am using VS 2010 SP1 Beta and ReSharper 5.1 C# Edition build 5.1.1727.12