asterisk users - Mar 2005 - X100P and Toshiba PBX

Hi all,

I'm dealing with a Toshiba PBX - DK 40 I think it is...The problem is this:

If someone dialing in from the PBX (on one of the two X100P cards) goes 
into a MeetMe conference...Everything is
fine, until they hang up - especially if there's music on hold - the 
line is held open because Asterisk does not know the
far end hung up.

I have it set to fxo_ls right now for signalling. But. I know that the 
PBX sends a DTMF tone of "A" upon connection,
and a DTMF tone of "D" upon disconnect...Is there anything I can do to
make Asterisk recognise these and disconnect?

Thanks,
-Matt