Beep to notify successful attended transfer

Hi !

I'm looking for a way to play a beep to the called phone, when it received an attended transfered call.

A calls B
B Att-Xfer to C
B speeks to C
"Beep needed here"
A speeks to C

I'm using Asterisk 1.8 and when i use the "attended transfert" features of Asterisk itself (*2), the beep works well.
But when i got to transfert the call with the phone, C speeks to B, then to A without any notification.

Is there a way to enable this notification ?

Thanks

./Kriss