[michael-ax]

fwiw, there's a switch in every ext. mic. jack.

plug in an un-wired connector, cut of the wiring post, smooth with a nail-file or put on a crowning drop of glue so it won't rip your bag and you're done.

[myself248]

Often these are software, though. Yes there's a switch, but it just tells the audio subsystem to automatically select the plugged-in mic. You can still tell it to select the screen-frame mic instead.

[deadbunny]

A software switch. You can test by pluggin in your unwired plug then go set to any program and select the internal mic and it'll work fine.