[TenTec] Omni 6+ mute?

[Barry N1EU]

Does anyone know a way to mute the Omni 6+ when in cw receive with an
external control line?

I just want to use Omni 6+ in receive mode, as an auxiliary receiver
tuned to the same frequency as the transmitting radio.  I've worked
out the antenna switching but I still need to mute the Omni 6+ while
the other radio is transmitting.  Any ideas or kludges?

Thanks & 73, Barry N1EU