I did this crudely using jQuery and your example
Check this fiddle:
I simply detected the direction of the scroll-wheel and pushed the horiz-scroll bar with jQuery
$(document).ready(function(){
$('#content').bind('mousewheel', function(e){
var curScroll = $("#content").scrollLeft();
if(e.originalEvent.wheelDelta > 0) {
$("#content").scrollLeft(curScroll-500);
} else {
$("#content").scrollLeft(curScroll+500);
}
});
});
It is "crude" because I hard-coded some values like the 500px amount to scroll, you could write some more javascript to detect dynamically how much to scroll. Plus I don't know if the wheelDelta value will be +120 for up and -120 for down, for you and other users.
Also note that the scrolLeft() can be animated.. for smoother transitions.