Your wireles doorbell method for power is pretty cool. I don't think I've seen that one before.
There are a couple other ways to do it. One is to follow the tuturials on
http://xbox-scene.com that have you modify your controller and add an extra button for power. This to me would be the best for a cab because you could go back to the "one button to rule them all" theory thats been discussed here many times.
There is also a simple no mod method that can be done to any xbox. That is to get a RF remote switched outlet (home depot has them) for about $12. Then plug your xbox into that. Take a paper clip or something similar and wedge it in next to your power button so that the power button is always depressed. Then you can turn it on and off with the remote outlet. This trick has often been used for tv's when you want to turn the tv on and off with a power strip. It won't hurt your xbox or void your warranty.