How do you add ID/Classes to wp_page_name list items

I’m using a single sprite for all the links in my menu and here’s my CSS

.nav li a {
	float:left;
	height:0;
	overflow:hidden;
	width:100px;
	padding-top:30px;
	background-image:url(images/nav.png);
	background-repeat:no-repeat;
}
.nav .page-item-5 a { background-position:0 0; }
.nav .page-item-3 a { background-position:-200px 0; }
.nav .page-item-2 a { background-position:-300px 0; }

.nav .page-item-5 a:hover { background-position:0 -30px; }
.nav .page-item-3 a:hover { background-position:-200px -30px; }
.nav .page-item-2 a:hover { background-position:-300px -30px; }

.nav .page-item-5 .current_page_item { background-position: 0 -60px; }
.nav .page-item-3 a.selected { background-position:-200px -60px; }
.nav .page-item-2 a.selected { background-position:-300px -60px; }

the issue with wp_page_menu is the class on the

• tag which means this line wouldn’t work:
  .nav .page-item-5 .current_page_item { background-position: 0 -60px; }

is there a way to add the current page class to the tag instead?
<li class="page-item-5 current_page_item"><a class="selected" ...>
or something to that effect?

TIA