asterisk users - Aug 2005 - How to force Requested transfer capability on BRI/PRI dial?

Hi,

on a configuration with one external ISDN S bus (to telco) and one
internal S bus (to ISDN telephone), where Asterisk is in the middle
(using HFC hardware), I noted the following:

   - when a GSM phone or ISDN phone calls in, the Transfer capability
     is Requested transfer capability: 0x00 - SPEECH

   - when an analog phone calls in (either from an analog line or
     an analog ISDN port), the Transfer capability is
     Requested transfer capability: 0x10 - 3K1AUDIO

The problem is that the ISDN phone in the internal bus apparently
ignores this transfer capability in the SETUP message: it does not
answer at all.  It works well in the first case (GSM, etc)

AFAIK there is no difference in the codec in both cases: just a type
difference. How can I make Asterisk (libpri?) force the Transfer
capability to the first value in any case ?

After looking a bit in the source (channels/chan_zap.c) and in
apps/app_settransfercapability.c it looks like I can do it
with in the call sequence (extensions.conf)

   SetTransferCapability('SPEECH')

Is there a better way ?

Thank you.