I'm overriding _renderMenu function in my solution:
_renderMenu: function( ul, items ) {
var that = this;
$.each( items, function( index, item ) {
that._renderItemData( ul, item )
.children("a")
.attr("title", item.value["@tooltip"])
.prepend("<img class='menu_button_img' src='" + item.value["@icon"] + "' /> ");
});
},
Works ok for me :)