Automatic demo login

Hey guys,

After the crossroads post, I thought about altering Aalborg's css a little bit to show you that we don't really need a completely new theme to have a more modern look, just by changing some subtle things.
I'd like to start working on it and later, show it in a demo install. Can someone provide me with a snippit so I can login my demo-user automatically?

I tried

elgg_authenticate('demouser','demouserpassword') 

of course, that user exists, but although it returns true, no login happens.