My airplane owner would like to be able to communicate with the cockpit or listen in on frequency. It's a ways back as he likes the right aft seat in the king air 350. I was thinking an external intercom box plugged into the co-pilot side with a 25 foot '"extender cables" to the aft of the plane to plug in his headset preferably something with an off switch. Another thought is a handheld com with an adapter so he can plug his headset into it and contact us on com #2. I am looking for some input before I start experimenting.