Could be simpler, but here is what I was wanting:

Code:
<script type="text/javascript">
jQuery(function(){
	if (document.cookie.indexOf("CustomerID") !=-1 ){
		var simplecheckout = '<input type="image" name="btn_checkout_guest" class="btn_checkout_guest" src="v/vspfiles/templates/223/images/buttons/btn_checkout_guest.gif">';
                $("#v65-cart-checkout-table").replaceWith(simplecheckout);
	}
});
</script>