Edit general_custom.xml, action_missed_url with global variable

hey,

if I add the following line

<action_missed_url perm=“R”>http://192.168.0.7/dnd_status.php?active_user=$active_user&dnd=missed</action_missed_url>

to my gneral_custom.xml, I got problems with the $active_user because of formatting… in this dnd_status.php script, I do need this parameter, any ideas how to handle this?