> There's now been reported a way to hack a computer by way of its microphone, so that particular method is out.

No, it's not. It's in some server in a datacenter. If you can get to the server, you can just change the Poker code, no need to do any crazy microphone hacking. Plus you'd need to know exactly when and how the microphone was sampled.

> CPU temperature doesn't change enough to serve as a secure source of entropy.

Doesn't matter how much it changes, the lowest bits are random on a large enough time scale.

You can just run the sampler until you get enough bits, it will take a few minutes. Or you can run it constantly and add more and more entropy as you go.