You can use event.target to identify if the scrolling element is the one you want to affect:
function stopWheel(e){
if (e.target.id === "slider-'.$question_id.'") {
if(!e){ e = window.event; } /* IE7, IE8, Chrome, Safari */
if(e.preventDefault) { e.preventDefault(); } /* Chrome, Safari, Firefox */
e.returnValue = false; /* IE7, IE8 */
}
}
Plus you need to provide the event in the first call:
document.onmousewheel = function (e) {
stopWheel(e);
} /* IE7, IE8 */
Here's an example: http://jsfiddle.net/Da3L3/