Unfortunately this isn’t possible (without a slight hack)- since there are no hooks provided (see for example the edit.php
page).
A quick and easy hack is to use JavaScript to add the link after the usual ‘Add New’ link. Here I’ve used the admin_print_footer_scripts
hook (on ‘post’, or ‘edit-post’ screens) to print the JavaScript. Note that you must alter this to work for other post types.
add_action('admin_print_footer_scripts','wpse57033_add_new_voucher_link');
function wpse57033_add_new_voucher_link(){
$screen = get_current_screen();
if( $screen->id == 'edit-post' || $screen->id == 'post' ){
?>
<script>
jQuery('.wrap h2 .add-new-h2').after('<a href="" class="add-new-h2">Add New Voucher</a>');
</script>
<?php
}
}