<a href="your-link-here" class="big-link">some link text</a>

和

a.big-link{position:relative;}
a.big-link:before{
    position:absolute;
    content:'';
    top:-10px;
    right:-10px;
    left:-10px;
    bottom:-10px;
}

演示于http://jsfiddle.net/kq8pq/2/