Using dahdi FXS port as media source: ignore offhook/onhook state

Hello

i have a special project here and i’m stuck with a problem
my customer has a very old PBX with a special equipment connected to the pbx using FXS port.
they need to keep this equipement but want’s me to install Asterisk pbx

this equipement is in a offhook state all the time.
and i need to “listen” the audio (and send audio) to this equipement time to time when a sip phone is used.

so i wanted to do this:
when a sip phone call someone, use a special context to add the sip phone to a confbridge room, then dial the number initialy dialed and add it also in the conf room. and then, add the dahdi fxs channel to the conf room also

my problem is : i can put “immediate=yes” to the FXS channel so as soon as asterisk see this channel is offhook, add it to the confbridge room.
but if asterisk is restarted, or even dahdi is restarted, asterisk don’t “see” that the fxs is offhook and so don’t execute the context (with immediate=yes)
this will be a problem because they cannot restart/disconnect the equipement each time dahdi/asterisk is restarted.

on some old pbx we had some option to ignore the state of a fxs port and assume it’s always offhook. it was often used to connect some equipement to use it as media source for MOH.
is it possible to do this with asterisk ?

if i can tell asterisk to ignore the state of the fxs port, and just listen/send the audio to the port, it would be perfect.
help :sob:

Asterisk 13.17.2
Dahdi 2.11.1

(ps: as a french i sometime write funny sentence in english. So if you did not understand ANYTHING of my problem, just tell me and i’ll try to explain better)