If you have a basically fixed set of numbers you transfer to, you should be able to define virtual extensions that are no-answer forwarded to a desired external number. Then, set these virtuals in an unused Timer Class in 20-29, set 20-31-15 to 1 or 2 seconds for that Timer Class. Users would transfer caller to virtual extension which would ring 1 or 2 seconds then forward off-premise. One second timing worked on SIP trunks.