How do you get an active expanded accordion menu to persist in an expanded state

I’ve got my Wayfinder accordion menu up and running, see here if you like. It’s the http://wiki.modxcms.com/index.php/Accordion_menu_with_Wayfinder_using_JQuery version. But with a hardcoded version of this menu it’s possible to get the active expanded menu element to stay open for every child document in the active parent document, by using <a href="[~xx~]&submenuheader=0">, see example here.

How can this be done in Wayfinder? How can I tell which submenuheader number thats active?