Custom fields as functions.php variables?

I currently let Pages appear in my main navigation bar by using the includes parameter of wp_list_pages, like so:

function sandbox_globalnav() {
	if ( $menu = str_replace( array( "\r", "\n", "\t" ), '', wp_list_pages('include=10, 2, 13, 91, 1324, 1405, 1356, 664, 1268, 1533, 1841&title_li=&sort_column=menu_order&echo=0') ) )

When a new page is made, I have to manually add the page ID to this list to allow it to show.

Can anyone offer a slicker way of doing it that won’t take long? I’m thinking there may be a way to collate a new Page custom fields setting into a global variable accessible to functions.php, which will create this list.

Thanks!
Matt