I do something similar but it doesn't help me with the built in microphone in the laptop. I'd have to disassemble the bezel and possibly snip a wire. It's much easier to Macgyver disable a webcam than a Microphone, even if you've got one of those webcams that can see through plastic with infrared. Best I can do so far is disable the device in device manager.

Although I wonder if the bios on this HP let's you disable it...