How to Set Speaker and Microphone Combination?

I use a headset or my desktop speaker combined with my webcam microphone for calls. When I am on a call and I click on the audio button to change the speaker and microphone settings there is a drop down for "Speaker and Microphone Combination". There is only one option there - my headset speaker and microphone. How do I create another "Speaker and Microphone Combination" so that I can select it from the drop down, to then use the webcam microphone and desktop speaker? I'd like to be able to easily switch back and forth between those two configurations.