Global parameter in general.xml


I’ve got 20 Snom370 phones connected to my asterisknow freepbx, so I edited the general.xml…
one entry in my general.xml should be:

<action_missed_url perm=“R”>$active_user&dnd=missed</action_missed_url>

so, the problem is, the global parameter $active_user is not allowed in this xml file… I need this parameter for my dnd_status.php script, any idea how to handle this?