asterisk users - Jan 2007 - automon and MONITOR_EXEC

I have been trying to get Asterisk to NOT mix the in and out files from an
auto-monitored call.  Something like this:

  exten => s,n,SetVar(MONITOR_EXEC=/bin/true)  ; do not delete files
  exten => s,n,Dial(Zap/r1/${EXTEN},,wW)

Pressing *1 records as it should, but the recording is always mixed at the
end of the call.

I have figured out that the monitor is being done to the callee channel
instead of the caller channel (where MONITOR_EXEC is set).  So when the
call ends, ast_monitor_stop looks for MONITOR_EXEC on the callee channel
and gets a null.

Does anyone know a workaround for this?  How can I set a channel variable
on the callee channel?

~ John Williams