UGS service flow for soft phone

Hello everybody,

I'm trying to build a config file which open a UGS sevice flow for soft phones.
As we know the UGS service flow is being opened by the MTA part of the CM and is not a part of the Docsis config file.
By know I can make the call only over the BE service flow which serves the HSD service.
can anyone help with an idea, how can I enforce the CMTS to open a UGS service flow via the config file?

Thanks in advance,
Asaf