[HELP]: Connect to loudspeaker system from zap extension

I have a loudspeaker amplifier that is connected to via a telephone plug. I would like to be able to plug it into a FXS port on my Sangoma card and use it as an extension.

The problem is that the line essentially always is “active” so any calls to this extension result in a busy signal. Is there a way to set an extension to simply “open” a Zap channel that is already active?

I know the alternative is to use soundcard output to the amplifier, but I would much rather work with the existing setup.