Icom A5 headphones wiring?

Does anybody know how to connect headphones (listen-only) to an Icom A5
handheld radio? It has a 3.5mm (1/8") jack, but the official thing to
plug in there is an adapter for aviation headsets (including mic & PTT),
and the plug of that adapter has 4 wires (tip & sleeve and 2 rings,
looks like an iPhone connector). Can I plug headphones into it, without
bypassing the internal mic & PTT? I'd build the needed adapter if
necessary, but need to know the wiring diagram. But if the physical
presence of the plug in that socket disconnects the internal mic & PTT
then the answer would be "no".