var img = new Image();
img.src = '/themes/yourTheme/images/ui-icons_whatever.png';
Note that this is done asynchronously, so the rest of the page may load before the image(s) finish loading- but at least they will (probably) load before the user triggers a hover or other event.
This should do the trick:
Note that this is done asynchronously, so the rest of the page may load before the image(s) finish loading- but at least they will (probably) load before the user triggers a hover or other event.