I suspect the tough part is going to be local monitoring. The remote host needs to be able to hear himself plus mix minus audio from the studio end.
That might be doable in the audio properties screen by checking “monitor this input,” or some such language, under the recording tab (win 7, etc.).
An external device (read: complication) might be needed such as, but not exactly, a Behringer UCA202. One problem with the ‘202: it needs a line level input.
The neat thing about it is that you can do input monitoring within the device by just turning on the monitor switch.
So you plug your headphone mini plug into the phones jack and you hear what’s coming back from the studio plus your own voice.
Alas, the mic audio would have to run thru a preamp before connecting to the input of the ‘202.
I haven’t looked further but there might be something like this out there that would do the same things except also have a mic level input.
Still it’s another added box but maybe only one...at least until a true USB headset comes along.