Need to be able to use the same extension from two phones?

I have two workstations in my office and would like to be able to switch seamlessly between them as I work the phones. I also use a power dialing service so my calls are served up to me one at a time. What I am thinking of is much like an old fashioned land line where you could listen in on your siblings calls from another phone in the house :-). Is there a way to do this or a work-around that I am not thinking of? My phone is a Polycom SoundPoint IP 335 and my headset is a Plantronics Savi W710 headset. (I have two identical sets of hardware)

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