Edit in JSFiddle

(function($, undefined) {
if (!$.uncamelCase) {
    // Convert camelCase to dashed
    $.uncamelCase = function(string) {
        return string.replace( /([A-Z])/g, '-$1' )
            .toLowerCase().replace( /^-/, '');
    };
}

// dispatch to data() and attr()
$.fn.dataAttr = function(key, value) {
    var $this = this,
        ret = this.data(key, value);
    
    if (typeof key == "object") {
        $.each(key, function(key, value) {
            $this.attr("data-" + jQuery.uncamelCase(key), typeof value in {string:1, number:1} ? value : '~defined~');
        });
    } else if (value !== undefined) {
        $this.attr("data-" + jQuery.uncamelCase(key), typeof value in {string:1, number:1} ? value : '~defined~');
    }
    
    return ret;
};

$(function() {
    $('#data').on('click', function(e){
        e.preventDefault();
        $(this).dataAttr('hello', "yeah");
    });

    $('#data2').on('click', function(e){
        e.preventDefault();
        $(this).dataAttr('hello', 1);
    });

    $('#data3').on('click', function(e){
        e.preventDefault();
        $(this).dataAttr('hello', {foo: true});
    });
});

})(jQuery);

<h1>Selectable updates</h1>
<p>
    <button id="data" type="button">$.dataAttr('hello', "yeah")</button>
    <button id="data2" type="button">$.dataAttr('hello', 1)</button>
    <button id="data3" type="button">$.dataAttr('hello', {foo: true})</button>
</p>

/* set background for elements with "data-hello" attribute */
[data-hello] { background-color: blue; }
[data-hello="yeah"] { background-color: green; }
[data-hello="1"] { background-color: orange; }

h1 {font-size: 1.2em; font-weight: bold; margin: 5px 0;}
h2 {font-size: 1.1em; font-weight: bold; margin: 15px 0 5px 0;}