[Asterisk-Users] Variable for extension that transferred the call?

[Paul Zimm]

Is there a variable available to use in my dial plan, that identifies 
the extension or callerid that
transferred the call?

I use valet parking to stack calls for an extension in their own parking 
lot.
I'd like the extension they use for valet park to be the same for all 
phones. That way I can
"program" a memory button on the phone without worrying if it's hooked 
up to the
correct extension.

My extensions are 3 digit and all begin with 8.

current . . . . . . . . . .
exten => _5XX,1,ValetParkCall(auto|8${EXTEN:1}|120|8${EXTEN:1}|1|default)
exten => *66,1,ValetUnParkCall(fifo|${CALLERIDNUM})

what I want . . . . . . . . . .
exten => 
*55,1,ValetParkCall(auto|${extension_that_transferred}|120|${extension_that_transferred}|1|default)
exten => *66,1,ValetUnParkCall(fifo|${CALLERIDNUM})