rspec users - Mar 2007 - Mocks & Stubs in spec_helper?

I have to stub out

   setup do
     request.stub!(:user_agent).and_return(''Mozilla'')
   end

in each context because my Rails application.rb relies on it (for IE  
reasons).

Is there a way to create mocks or stubs in spec_helper.rb so I don''t  
have to repeat this?

Thanks,

Steve