You could do something similar by using a solid with a mask on it, combined with AE's Convert Audio To Keyframes command. The keyframes could drive the scale of the solid, which could then be used as a track matte. You could even put a mask on the solid.
But you wouldn't have to fool with animating the scale of a mask, which can be a Right Royal Pain.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA