I am currently playing around with the HybridSessionBuilder class found on Jeffrey Palermo\'s blog post:
http://jeffreypalermo.com/blog/use-this-nhibernate-wrapper-t
Just found a clean solution using Unity to inject a session per request:
http://letsfollowtheyellowbrickroad.blogspot.com/2010/05/nhibernate-sessions-in-aspnet-mvc.html