Parallax Effect without the use of background-attachment:fixed

Question

So I am trying to create a parallax style site much like this one. However, whereas they use background images with a 'fixed' attachment for the effect of the image not moving, I would like to use a jquery slideshow plugin. Basically, how can I achieve the 'fixed' attachment and background position of my images if they are contained in a slider? Currently the images in the slideshow just scroll through...

I'm happy to provide code samples slash any further information needed along the way

Thanks!