It appears from this question it is possible, you just need to add a title attribute. In which case this should work:

function dynAddOption(list, elementToBeAdded){
    if (list.length > 0) {
        for(var index = 0; index < list.length; index ++) {
            var opt = new Option(list[index].description, list[index].id);
            opt.title = 'Foo'; // < this is the tooltip
            elementToBeAdded.options[index + 1] = opt;
        }
    }
}