borrowing heavily from http://github.com/scottgonzalez/jquery-ui-extensions/blob/master/autocomplete/jquery.ui.autocomplete.html.js, this extension adds support for a callback function for building the text of the item label.

gistfile1.txt

(function ( $ )) {
  $.ui.autocomplete.prototype._renderItem = function (ul, item) {
    var text = (this.options.label) ? this.options.label( item ) : item.label;
    return $( "<li></li>" )
	.data( "item.autocomplete", item )
	.append( $( "<a></a>" )[ this.options.html ? "html" : "text" ]( text );
	.appendTo( ul );
  }
}