I tried to do it with opacity but I was having trouble with the Javascript. I came up with this, though.
It isn't exactly what you're looking for but I think it's pretty close with much less hassle and no Javascript.
I would use the :before
and :after
elements on a container to make gradients at the top and bottom of the element so it sort of fakes the opacity.
Here's a quick demo: http://jsbin.com/aVaSIJuB/1/edit?html,css,output