2 line headset with common mic?

I'm looking for a headset with Line 1 in the left ear and Line 2 in the right ear. The mic of course is for both lines. That way you can mute one line and still hear what they are saying and also, by not using the Mute function, let Line 1 know you are there and they then don't feel like they're just floating in a phone vacuum "on hold". I've found people tend to wait on hold almost indefinitely if they feel you are just about to get to them. If this headset design is not available, would it be difficult to just wire a binaural headset up to accomplish the same? Mic is wired to both lines and each line for each ear. This would use 2 telephones of course so you have 2 dialpads operational at all times.