Hint/state_interface of public number in local queue

Hi,
I’m looking for information how to build queue. I have to put an public number as queue member and this part is easy. I have to put local channel with this number as interface like, local/PSTN@dialout-queue

But how to configure queue to set property state of interface to know that if this channel is ‘not in use’, ‘ringing’ or ‘inuse’. This is possible ?

I solved my problem with custom hints. For member i set state_interface like Custom:PSTN_NUMBER and then in dialplan i used Set(DEVICE_STATE(Custom:PSTN_NUMBER)=RINGING/NOT_INUSE/INUSE) and it works as i want, i see in queue show command status of public number in my queues