asterisk users - Jun 2005 - Digit Map for IP500 - prepend digits from phone

via google, I found the reference regarding digit maps for the Polycom phones:
http://lists.digium.com/pipermail/asterisk-users/2005-January/082884.html

But, I don't see how to "prepend" a digit(s) to a number dialed
(from the
phone, not in an Asterisk extensions file).  For instance, I have several 
trunks.  Each trunk can be manually dialed by dialing a specific number in 
front of the number you are dialing.  I would like to set up the line 
appearances such that if I select the 3rd line appearance and dial 
1+AC+7digits, the phone will actually send  the prepend number and number 
dialed. i.e. dial 1-210-555-1212, the phone will send 8-1-210-555-1212.  I 
was able to do this pretty easily with the Sipura 841's.  I haven't
figured
it out yet with the Polycoms.

Thanks,
Doug