Found the solution myself, I’ll post it for anyone interested:
//Use the alternative index title specified in page options
function fm_alternative_index_title($title) {
//Only if currently looping
if(in_the_loop()) {
$page = get_page_by_title($title);
if ($p = get_post_meta($page->ID, "_x_entry_alternate_index_title", true)) {
$title = $p;
}
}
return $title;
}
add_filter('the_title', 'fm_alternative_index_title', 10, 1);