Background image stretch y-axis only, keep repeat-x

I have an image set as a background image of a div. The DIV size is changing and inside their is the image which is a gradient.

CSS:

#scroller_shadow{
    background-image:url(../img/ui/shadow.png);
    background-repeat:repeat-x;   
    background-position:top;
}

I need a cross-browser solution for making the image fit the height of the div in the y-axis only, keeping the repeat-x. The DIV is being resized dynamically via JQuery.

Their might be a cross-browser option using JQuery. I don't mind using scripts to achieve that in order to get cross-browser support (IE7+). I don't want to stretch the image because it loses the intensity when you stretch the image on the x-axis, making a semi-transparent png image almost transparent.

Thanks.