[Freeswitch-users] prevention of duplicate calls.

is there a method using xml that i can prevent callers three waying themselves. I find some idiots will do this so they can "produce" feedback into a conference room. I would like the system to automatically determine that they are already on the ivr and send them to a recorded message and hangup. or maybe auto hanging up the first call in case of "accidentals" from voips not hanging up  and continuing the first call.