You may use template_redirect
action:
add_action( 'template_redirect', 'wpse131387_template_redirect' );
function wpse131387_template_redirect( ){
if ($_SERVER['REQUEST_URI'] == '/some-template') {
global $wp_query;
$wp_query->is_404 = false;
status_header(200);
include(dirname(__FILE__) . '/some-template.php');
exit();
}
}