* The body is engaged in a monotonous, mundane, or repetitive activity, freeing the mind to think about other things
* The environment is changed
Another activity that fits these requirements is running. It also has the added benefit of physical exercise.
You know the iPhone headphones, the ones that have a little microphone built into the side? It acts as a button, as well (I'm not sure if it's a soft button, though.)
I imagine that, if it were a soft button, someone could write, quite simply, a voice recorder program whose recording was toggled by that button. You could leave music running in the background, with the recorder running in the foreground, then press the button (both temporarily pausing the music at starting the recording), dictate your thought, and press the button again, at which point the music would resume.