[Elecraft] Listening to VFO A and VFO B

[RCStimson]

     When I work DX, I like to listen to VFO B and VFO A at the same time, but at different volume levels.  I want to hear the DX call me on VFO A and I like to find an open spot on VFO B where everyone is calling the DX station.
     Can I do that with my K3?  I don't see any obvious way, other than the not-yet-released Sub Receiver/  Maybe I missed that part of the Owners Manual.
                       Roger K8RS K3 #280.