Background properties – need a solution

Hi,

I am putting this one out there as I have not been able to crack it for a while!! I want to do a similar thing to the biffy clyro website with the way background work – http://www.biffyclyro.com/

I have set it up so that it is no-repeat and attachment is fixed but if you zoom out of the browser the background stays the same – on the example above the background stays the same – anyone know how this can be achieved?

Thanks