I'm sorry to say this, but you will not get such info here. Poly does not even provide pinout for that cable nor does support extending it's range.
And that port is dedicated only for Expansion Mic, nothing else.
Your best solution would be either using Poly Sync 40/60 (maybe dual - two devices wirelessly daisy-chained) or some third-party USB solution. If you connect both to a USB hub, then you will have only one USB cable to your PC.
Just keep in mind, that each and every time you will have to manually choose input device for microphone (since Studio USB has both mics and speakers built-in, those will probably have higher priority when discovered by Windows).
Hope that helps.