> parser.add_argument('--license', action='write', message='...', file=sys.stdout)
The ability to redirect the output would be a nice addition.

> parser.add_argument('--license', action='call', callable=lambda: sys.stdout.write(message)) 
optparse already has a 'callable' action, I had the impression it was left out of argparse on purpose, even tough I couldn't imagine why...

Either way is fine for me.