How can I disable session state in ASP.NET MVC?

I would like to have a very lightweight ASP.NET MVC site which includes removing as many of the usual HttpModules as possible and disabling session state. However when I try to do this, I get the following error:

The SessionStateTempDataProvider requires SessionState to be enabled.

I've disabled session state in web.config:

<sessionState mode="Off" />

I understand that ASP.NET MVC uses session state for TempData, but I don't need/want TempData - I just want to disable session state. Help!