Enable both headset and speaker audio connections at the same time

I'm using a computer with a Realtek 6.1-channel onboard audio and I want to be able to use my headset-mic with the desktop speakers at the same time. I work as a virtual assistant with only a few calls coming in. Rather than sit in front of my computer the entire work shift, I want to be able to leave the computer without having to miss a call coming in through Skype. However, with my headset-mic device plugged in, the speakers are automatically disabled. I have the headset plugged into the green audio port, while the speakers are plugged into the black port. How do I enable both devices to work simultaneously so I can hear the ringing through the speakers when a call comes in through Skype while I am away from the computer?

