[Freeswitch-users] mod_callcenter and moh-sound

The wiki says you can use the channel variable ${hold_music} (http://wiki.freeswitch.org/wiki/Mod_callcenter#moh-sound) Yet when you use <param name="moh-sound" value="${hold_music}"/> You will get: mod_native_file.c:74 Error opening /usr/local/freeswitch/sounds/en/us/callie/${hold_music}.PCMU If you use <param name="moh-sound" value="$${hold_music}"/> It will play the hold music set in the global variable. Is there any way for mod_callcenter to take a channel variable as the music on hold?