Press the '2' key. Or any other number if you feel like messing with the machine.
I happened to try that one time, it wasn't even announced in the recording and it said that I would be removed from their list.
It's worth a shot, right?
If that doesn't happen then the recording might stop or start over again.
eta: Bad A Billy mentioned about politicians are exempt from the Do Not Call List, but charities are also exempt. And 100% of the time this has always been a real person that calls, saying they're from ACS Services, or for the Highway Patrol, or whatever. The moment I hear them say they organization they're calling for - I simply hang up. There's no use in wasting either of our time.